Status of Wetlands in Bangalore


 Wetlands are one of the most productive ecosystems, comparable to tropical evergreen forests in the biosphere and play a significant role in the ecological sustainability of a region. They are an essential part of human civilisation meeting many crucial needs for life on earth such as drinking water, protein production, water purification, energy, fodder, biodiversity, flood storage, transport, recreation, research-education, sinks and climate stabilizers. The values of wetlands though overlapping, like the cultural, economic and ecological factors, are inseparable. The geomorphological, climatic, hydrological and biotic diversity across continents has contributed to wetland diversity.  Across the globe, they are getting extinct due to manifold reasons, including anthropogenic and natural processes. Burgeoning population, intensified human activity, unplanned development, absence of management structure, lack of proper legislation, and lack of awareness about the vital role played by these ecosystems (functions, values, etc.) are the important causes that have contributed to their decline and extinction.  With these, wetlands are permanently destroyed and lose any potential for rehabilitation. This has led to ecological disasters in some areas, in the form of large-scale devastations due to floods, etc.

 Figure 1: The Hydrological Cycle

            The hydrological cycle (Fig.1) is one of the key elements in the aquatic environment. Water (moisture) constantly revolves between the ocean, sky, land and the ocean again. Water in the oceans evaporates into the atmosphere, and falls back on the earth as precipitation, some of which after wetting the foliage and ground, run off over the surface to lakes and rivers. Excess water causes floods and erosion. Precipitation that soaks into the ground is available for growing plants and evaporation. It also reaches the deeper zones and slowly percolates and seeps out to maintain the water level in the streams during dry periods. The global water cycle unifies the subsystems consisting of state variables (precipitable water, soil moisture, etc.) and fluxes (precipitation, evaporation, etc.).

         Wetland ecosystems depend on constant, recurrent or shallow inundation at or near the surface of the substrate and characterise the presence of physical, chemical, and biological features (grade continuously from aquatic to terrestrial), identified by hydric soils and hydrophytic vegetation. Water, modified substrate and distinct biota thus are the essential constituents of these ecosystems.

         Wetlands form the transitional zone between land and water, where saturation with water is the dominant factor determining the nature of soil development and the types of plant and animal communities living in and on it (Cowardian et al., 1979). They are usually formed in the depressions (subjected to flooding) and groundwater seeps. Wetland type is determined primarily by local hydrology and the unique pattern of water flow through an area. In general, there are two broad categories of wetlands: coastal and inland. Enhanced appreciation of wetlands in the recent past has led to the signing of many international agreements for protecting them, among which the Ramsar convention is the most important.

The Ramsar Convention on Wetland[1] in 1971, in Iran( wetlands as

'... areas of marsh, fen, peatland, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six meters.'

Figure 2: Graph showing water distribution on earth



 [1] Mission Statement: "The Convention's mission is the conservation and wise use of wetlands by national action and international cooperation as a means to achieving sustainable development throughout the world" (Brisbane, 1996). ( ).

        The Ramsar Convention is an intergovernmental treaty, which provides the framework for national action and international cooperation for the conservation and wise use of wetlands and their resources. There are presently 127 contracting parties to the Convention, with 1085 wetland sites, totaling 82.2 million hectares, designated for inclusion in the Ramsar List of Wetlands of international importance.











Two-thirds of the earth is surrounded by water and appears blue (the planet of water) from space (UNEP, 1994). Lakes and rivers, the most important freshwater resources, account for 2.53% of the total water found on earth (Figure 2). Of the total water in the hydrosphere (4 x 108 cubic kilometres), 97.5% is deposited in the oceans that cover 71% of the earth’s surface. Wetlands are estimated to occupy nearly 6.4% of the earth’s surface, 30% of which is made up of bogs, 26% fens, 20% swamps, about 15% flood plains, etc. (IUCN, 1999). The amount of fresh water on earth is very small compared to seawater, of which 69.6% is locked away in the continental ice, 30.1% in underground aquifers, and 0.26% in rivers and lakes. Lakes in particular occupy less than 0.007% of the world’s fresh water. The distribution of the world water resources compiled from various sources is listed in Table 1 and the continent wise distribution of fresh water resources is listed in Table 2 (UNEP 1994).


Table 1: Distribution of world water resources


WaterResource Area( Volume( %  total water % Fresh water    
Ocean 361 1338 97.47
Fresh water -- 35 2.53
Ice  16 24 1.76 69.1390
Ground water -- 10.5 0.76 30.0710
Wetlands (marshes, swamps, lagoons, flood plains, etc.,) 2.6 0.1 0.0001  0.0039
Lakes  (excluding saline lakes) 1.5 0.09 0.007  0.2769
Rivers -- 0.02 0.0002  0.0079


Table 2: Distribution of fresh water resources by continents

Fresh water type Africa Europe Asia Australia North America South America
Lakes* 30,000 2,027 27,782 154 25,623 913
Rivers* 195 80 565 25 250 1,000
Reservoirs* 1,240 422 1,350 38 950 286
Ground water* 5,500,000 1,600,000 7,800,000 1,200,000 4,300,000 3,000,000
Wetlands** 341,000 -- 925,000 4,000 180,000 1,232,000

        Wetlands with a share of 0.0001 % among the global water sources include swamps, marshes, bogs and similar areas and are an important and vital component of the ecosystem (IUCN, 1996). A wide variety of wetlands exist across the continents because of regional and local differences in hydrology, vegetation, water chemistry, soils, topography, climate and other factors. At the earth’s surface, fresh water forms the habitat of large number of species. These aquatic organisms and the ecosystem they live in represent a substantial sector of the earth’s biological diversity.


        The various beneficial functions of wetlands like sustaining life processes, water storage (domestic, agricultural and industrial usage), protection from storms and floods, recharge of ground water, water purification, storehouse for nutrients, erosion control and stabilisation of local climate (such as temperature and rainfall), help maintain the ecological balance.


        In their natural condition, most wetlands store floodwaters temporarily, protecting downstream areas from flooding. By checking the floods, they maintain a constant flow regime downstream, preserve water quality and increase the biological productivity of the aquatic communities. This function becomes increasingly important in urban areas, where developmental activities (such as breaching of wetlands for residential, commercial, and industrial activities, paving of surfaces in catchment areas, etc) have increased the rate and volume of surface water run-off and the potential for flood damage. This necessitates the protection of wetlands, an important means of minimising flood damages in the future.


        Periodically inundated wetlands are very effective in storing rainwater and have innate capacity to recharge the ground waters. Ground water recharge occurs through mineral soils found primarily around the edges of wetlands. The extent of groundwater recharge depends on the type of soil and its permeability, vegetation, sediment accumulation in the lakebed, surface area to volume ratio and water table gradient.


        Wetlands have a tremendous ability to meet the water requirement in the surrounding areas. Natural wetlands are underlain by aquifers with a high potential for water supply.


Wetland vegetation can reduce shoreline erosion in several ways, including –

·         Increasing durability of the sediment through binding (with stilt / plank root structure).

·         Dampening waves through friction.

·         Reducing current velocity through friction, improving water quality.

Coastal wetlands particularly mangroves help in shoreline stabilisation and storm protection by dissipating the force by reducing the damage of wind and wave action.


        Wetlands play an important role in improving the water quality by filtering sediments and nutrients from surface water. Aquatic vegetation helps in removing 90% of the dissolved nutrients like nitrogen and phosphorus and also in adsorption of heavy metals. Dissolved materials may be retained in wetlands and the water quality may vary seasonally or from year to year. Removal of sediment load is also valuable because sediments often transport absorbed nutrients, pesticides, heavy metals and other toxins that pollute the water.


        Wetlands, transition zones between land and water are efficient in filtering sediments. They can intercept run-off from land before it reaches the water and help in filtering nutrients, wastes and sediments from floodwaters. In certain wetlands, plants are so efficient in removing wastes that artificial wastewater treatment systems use aquatic plants for the removal of pollutants from water. Wetlands remove nutrients (especially nitrogen and phosphorus), particulates and total biological oxygen demand from flooding waters for plant growth and help prevent eutrophication or over-enrichment of other forms of natural waters (Nixon & Lee, 1986). However, overloading a wetland with nutrients, beyond its threshold, impairs its ability to perform basic functions.


        Wetlands being one of the most biologically productive natural ecosystems are vital for the survival of diverse flora and fauna, including many threatened and endangered species by providing shelter, food, etc., and forming a part of the complex food-web. It is estimated  (Wetlands in Asia, 1997) that about 20% of the known species of life rely directly or indirectly on wetlands for their survival, as they are their primary and important seasonal habitats.


        Wetland products include fish, timber, housing materials such as reeds, medicinal plants, the provision of fertile land for agriculture (sediments), water supply for domestic, arable, pastoral or industrial purposes, energy resource (fuelwood, etc), transport, recreation, tourism, etc. By supporting diverse human activities, large wetlands play a particularly important role in the subsistence and development of thousands of people.

In economic terms, these could be categorised into direct and indirect benefits.

  ·         Direct economic benefits include water supply, fisheries, agriculture, energy resource, wildlife resource, transport, recreation and tourism, supporting a vast diversity of flora, fauna and cultural heritage.

·         Indirect benefits are improved water quality (including drinking water) by intercepting surface runoff and removing or retaining its nutrients, processing organic wastes, reducing sediment before it reaches open water, and cultural aspects.


        Wetlands represent dynamic natural environments that are subjected to both human and natural forces. Natural events influencing wetlands include rising sea level, natural succession, hydrologic cycle, sedimentation, and erosion. The rise in sea level, for example, both increases and decreases the wetland’s spatial extent depending on local factors.

        Wetlands are under increasing stress due to the rapidly growing population, technological development, urbanisation and economic growth. Additional pressures on wetlands from natural causes like subsidence, drought, hurricanes, erosion etc., and human threats coming from over exploitation, encroachment, reclamation of vast wetland areas for agriculture, commercial and residential development, and silviculture have altered the rate and nature of wetland functions particularly in the last few decades. The primary pollutants causing degradation are sediments, nutrients, pesticides, salinity, heavy metals, weeds, low dissolved oxygen, pH and selenium (USEPA, 1994).

         Wetland loss may be defined as “the loss of wetland area, due to conversion of wetland to non-wetland areas as a result of human activity” and wetland degradation is “the impairment of wetland functions as a result of human activity”. About 50 % of the world’s wetlands have been lost in the last century, primarily through drainage for agriculture, urban development and water system regulations. It has been estimated that nearly one hectare of the world’s wetlands is getting degraded at the tick of every minute of the clock. (Narayanan, 1992).

Wetlands have been degraded and lost in ways that are not as obvious as direct physical destruction or degradation. Other threats include chemical contamination, excess nutrients, and sediment from air and water. On a global scale, climate change could also affect wetlands through increased air temperature; shifts in precipitation; increased frequency of storms, droughts, and floods; increased atmospheric carbon dioxide concentration; and sea level rise (Table 3). The loss of wetlands can be mainly attributed to natural and anthropogenic activities.

Table 3: Contribution of various sectors to pollution of wetlands

Anthropogenic Activities Industrial Domestic Agriculture Urbanization
Discharges to Wetlands ü ü ü ü
Non-point Source Pollution ü ü ü ü
Air pollutants ü X X ü
Toxic chemicals ü ü ü X
Deposition of fills material ü ü ü ü
Construction X ü X ü
Tilling for crop production X X ü X
Pest species of plants and animals X ü ü X
Siltation ü ü ü ü
Changing nutrient levels ü ü ü X
Tourism and recreational activities X X X ü
Water regime and physical modification ü ü ü ü


Apart from pollution, the other major problems include hydrologic manipulations of wetlands in the form of flow alterations and diversions, disposal of dredged or fill material, sewage inflows, and construction of levees or dykes leading to alterations in:

·         Water currents, erosion or sedimentation patterns;

·         Natural water temperature variations;

·         Chemical, nutrient and dissolved oxygen regime of the wetland;

·         Normal movement of aquatic fauna;

·         pH of the wetland; and

·         Normal water levels or elevations.

All of these impacts affect the wetland quality, species composition and functions.

Some activities do however create wetlands. Construction of farm ponds and in some cases, reservoirs and irrigation projects may increase wetland spatial extent, although valuable natural wetlands may be destroyed in the process.

Wetlands near urban centres are under increasing developmental pressure for residential, industrial and commercial facilities. Increasing population and economic growth create high demand for real estate in sub-urban localities. As suitable upland becomes exhausted, pressure intensifies to develop wetlands for residential housing, manufacturing plants, business office complexes and similar uses. They are often the final refuge for wildlife in an increasing urban environment and support many upland animals displaced by development. With accelerating development of adjacent uplands, the role of urban wetlands in flood protection and water quality maintenance becomes critical. Urban and industrial development increases the amount of surface water run-off from the land after rainfall. This raises flood heights and increases the flow rate of rivers, increasing the risks of flood damage. Increased run-off brings with it various substances that degrade water quality, such as fertiliser chemicals, grease and oil, road salt, sediment, etc. Effluents from some sewage treatment plants built to handle the needs of growing communities also reduce water quality. But, passing through wetlands, cleansing action takes place as many pollutants are removed, retained or utilised by the wetlands. Urban wetlands in certain instances function as recharge areas. This is especially true in communities where ground water withdrawals are heavy. Thus, urban wetlands are essential for preserving public water supplies.

In many cases, they represent the last large tracts of open land and are vulnerable to development for several reasons including the following:

·         Increased population in metropolitan areas has raised land values and demand for real estate.

·         Interstate highways have improved access to many areas, which has increased development opportunities.

·         Wetlands may be zoned for light industry or residential housing by local governments.

·         The lack of any comprehensive wetland protection policy measures for inland wetlands in most states.


The dominant features underlying wetland loss are population growth and subsequent anthropogenic developmental activities, which impose great pressure on water resources. Lack of appreciation of wetland values, their products, functions and attributes has led to conversion of wetlands for other purposes.

The unsustainable use of wetland resources may be considered to be a combination of information, market and policy or intervention failures. The information failure refers to the widespread lack of appreciation of the economic values of conserved wetlands. The market failure is the external problem whereby wetlands are damaged by economic activities without accounting for direct and indirect benefits of these ecosystems.

The loss or degradation of wetlands can lead to serious consequences, including increased flooding; species decline, deformity, or extinction; and decline in water quality. These losses, as well as degradation, have resulted in greatly diminishing the wetland resources across all continents of which the loss of fish diversity is conspicuous.  Besides, wetlands are also important as a genetic reservoir for various species of plants including rice, which is a staple food for 3/4th of the world's population. The spatial loss of wetlands means broader ramifications to life on earth through loss in food chain links.  

The quality of water flowing into wetlands may be impaired indirectly, by alterations to the water regime or by different types of polluting activities. Pollution of inland waters is mainly due to the discharge of domestic sewage, industrial wastewaters and agricultural operations. Pollution can be classified as point source (emanating from an identifiable source) or non-point pollution (emanating from a diffuse source). The wastewater coming from point sources are easier to treat than that from non-point sources.  The effects of diffuse pollutants are cumulative and can adversely affect wetlands even at some distance. Lower water quality results in degradation or destruction of wetlands.

 Decline in wetland quality results in increased undesirable growth of weeds and algal blooms. When these algal blooms decompose, large amounts of oxygen are used up, depriving fish and other aquatic organisms of oxygen resulting in their death.

 The extraordinary productivity of water ecosystems means that many different stakeholders or users have easy access to and use of wetland resources. The overexploitation of these resources entails intense cropping, overgrazing, over fishing and excess hunting pressure. The cumulative impacts of these activities threaten biodiversity.

 Water plays an important role in the development of a country. In India, where majority of the population is agrarian, quantity and quality of aquatic resources play a major role in the ecological and economic sustenance of the people.  


India is blessed with water resources in the form of numerous rivers and streams. By virtue of its geographical position and varied terrain and climatic zones, it supports a rich diversity of inland and coastal wetlands. Wetlands distributed from the cold arid Trans-Himalayan zone to wet Terai regions of Himalayan foothills and Gangetic plains extend to the floodplains of Brahmaputra and swamps of northeastern India including the saline expanses of Gujarat and Rajasthan. Along the east and west coasts they occur in the deltaic regions to the wet humid zones of Southern peninsula and beyond, to the Andaman and Nicobar and Lakshadweep Islands. India also shares several of its wetlands with Ladakh and the Sunderbans deltas with Bangladesh. These wetland systems are directly or indirectly associated with river systems of the Ganges, Brahmaputra, Narmada, Tapti, Godavari, Krishna and Cauvery. Southern peninsular India has very few natural wetlands, although there are a number of man-made water storage reservoirs constructed virtually in every village known as ‘tanks’ providing water for human needs and nesting sites for a variety of avifauna.


India has totally 67,429 wetlands, covering an area of about 4.1 million hectares [Ministry of Environment and Forests (MoEF), 1990]. Out of these, 2,175 are natural and 65,254, man made. Wetlands in India (excluding rivers), account for 18.4% of the country’s geographic area, of which 70% is under paddy cultivation.

 A survey conducted by the Ministry of Environment and Forests (MoEF) in 1990 showed that wetlands occupied an estimated 4.1 million hectares of which 1.5 million hectares were natural and 2.6 million hectares manmade (excluding paddy fields, rivers and streams) and mangroves occupying an estimated 0.45 million hectares. About 80% of the mangroves were distributed in the Sunderbans of West Bengal and Andaman and Nicobar Islands, with the rest in the coastal states of Orissa, Andhra Pradesh, Tamil Nadu, Karnataka, Kerala, Goa, Maharashtra and Gujarat. According to the Directory of Asian Wetlands (1989), wetlands occupy 58.2 million hectares or 18.4% of the country’s area (excluding rivers), of which 40.90 million hectares (70%) are under paddy cultivation (Figure 3). A preliminary inventory by the Department of Science and Technology, recorded a total of 1,193 wetlands, covering an area of about 3,904,543 ha, of which 572 were natural (Scott and Pole, 1989). The Directory of Indian Wetlands published by WWF and Asian Wetland Bureau in 1995 records 147 sites as important of which 68 are protected under the National Protected Area Network by the Wildlife Protection Act of 1972. State-wise distribution of wetlands in India (Chatrath, 1992) is given in Table 4.


Table 4: Distribution of wetlands in India

Sl.No State


    Nos. Area (ha) Nos Area (ha)
1 Andhra Pradesh 219 1,00,457 19,020 4,25,892
2 Arunachal Pradesh 2 20,200 NA NA
3 Assam 1394 86,355 NA NA
4 Bihar 62 2,24,788 33 48,607
5 Goa 3 12,360 NA NA
6 Gujarat 22 3,94,627 57 1,29,660
7 Haryana 14 2,691 4 1,079
8 Himation Pradesh 5 702 3 19,165
9 Jammu and Kashmir 18 7,227 NA 21,880
10 Karnataka 10 3,320 22,758 5,39,195
11 Kerala 32 24,329 2,121 2,10,579
12 Madhya Pradesh 8 324 53 1,87,818
13 Maharashtra 49 21,675 1,004 2,79,025
14 Manipur 5 26,600 NA NA
15 Meghalaya 2 NA NA NA
16 Mizoram 3 36 1 1
17 Nagaland 2 210 NA NA
18 Orissa 20 1,37,022 36 1,48,454
19 Punjab 33 17,085 6 5,391
20 Rajasthan 9 14,027 85 1,00,217
21 Sikkim 42 1,107 2 3
22 Tamil Nadu 31 58,068 20,030 2,01,132
23 Tripura 3 575 1 4,833
24 Uttar Pradesh 125 12,832 28 2,12,470
25 West Bengal 54 2,91,963 9 52,564
  TOTAL 2167 14,58,580 65,251 25,87,965 Union Territories Natural      
1 Chandigarh -- -- 1 170
2 Pondicherry 3 1,533 2 1,131
  TOTAL  3 1,533 3 1,301
  GRAND TOTAL 2,170 14,60,113 65,254 25,89,266

Table 5: Distribution of mangroves in India

Sl No States / Union Territories Area in sq. km
1 Andaman and Nicobar Islands 1190
2 West Bengal 4200
3 Orissa 150
4 Andhra Pradesh 200
5 Tamil Nadu 150
6 Karnataka 60
7 Goa 200
8 Gujarat 260
9 Maharashtra 330
  TOTAL 6,740

India accounts for 16% of the world’s population in 2.42% of the earth's surface. About 74% of human population is rural (HDR, 1999) and subject wetlands to stress from various anthropocentric activities. Human communities in India are closely associated with wetlands since the Indus valley civilization, which flourished along the banks of river Indus. The water bodies and their resources have been an integral part of the social and cultural ethos of human societies. Currently about 170 million people constituting 17% of India’s total population in more than 3,800 coastal villages are scattered along the 7,500 km coastline. Communities living close to wetlands follow the natural cycle of floods and adjust to the seasonal movements of the fish and harvest them based on changing water levels. The coastal villages, due to poor resource base and livelihood insecurity force an unsustainable dependence on coastal wetlands and change their characteristics leading to their destruction.  Marine fisheries in the Arabian Sea and the Bay of Bengal, export approximately 307,337 tons of fish annually and about two thirds of this export is made up of shrimp (Ministry of Fisheries, 1999). In addition to the various ecological and economic values, wetlands also provide cultural value to societies. Most of the Indian villages are settled around dependable water sources for drinking, etc.


Wetlands have been drained and transformed by anthropogenic activities like unplanned urban and agricultural development, industrial sites, road construction, impoundment, resource extraction, and dredge disposal causing substantial long-term economic and ecological loss. Of the total aerial extent of 58.2 million ha, nearly 40.9 million ha is under paddy cultivation. About 3.6 million ha is suitable for fish culture, while approximately 2.9 million ha is under capture fisheries (brackish and freshwater). Mangroves, estuaries and backwaters occupy a spatial extent of 0.4, 3.9 and 3.5 million ha respectively. Man-made impoundments contribute about 3 million ha. Rivers, including main tributaries and canals, occupy nearly 28,000-km. Canal and irrigation channels contribute to 113,000-km.

 Though accurate results on wetland loss in India are not available, the Wildlife Institute of India conducted a survey on these aspects and revealed that 70 – 80 percent of individual fresh water marshes and lakes in the Gangetic flood plains have been lost in the last five decades. At present, only 50 percent of India’s wetlands remain. They are being lost at a rate of 2 to 3% every year. Indian mangrove areas have been halved almost from 700,000 hectares in 1987 to 453,000 hectares in 1995 (Sustainable Wetlands, Environmental Governance-2, 1999).

The Directory of Indian Wetlands published by the World Wide Fund for Nature (WWF)-India and Asian Wetland Bureau in 1995 records 147 wetland sites. About 32% of these sites were lost primarily through hunting and associated disturbances, while 22% were lost to human settlements, 19% to fishing and associated disturbances, and 23% through drainage for agriculture. Removal of vegetation in the catchment leads to soil erosion and siltation that is estimated to contribute to over 15 % of wetland loss. Nearly 20 % of wetlands have been lost mainly due to pollution from industries (WCMC, 1998). T[ERG CES1] he recent estimate based on remote sensing shows only 4000 sq. km area of mangrove resource in India. The current rate of wetland loss in India could lead to serious consequences as large populations are dependent on these wetlands (World Development Report, 1994).

 Some of the major threatening factors influencing wetland destruction in India include:

 Hydrologic alteration

Wetlands consist of multiple linked paths (waterways, habitat types, biodiversity on the site) that interact through energy flows, chemicals and physical transfers, moving biota, and water flows. Watershed conditions and downstream wetlands are linked as they influence the soil and hydrologic regime of the downstream areas. India’s entire land surface has been altered through long-term human use and manipulations (e.g., intensive cropping, deforestation, intensive grazing and alteration of water flows). Anthropogenic alteration of the hydrological regime has further led to the alterations in natural drainage (Gopal, 1982). For example, map analysis of different periods by Rao & Sadakata (1993) showed sediment split 30 km long at the mouth of the northernmost river tributaries of Godavari in South India. Rivers continue to be isolated from their neighbouring floodplains leading to lowered water tables, loss of ground-water recharge, human development in flood prone areas and increased flooding potential downstream due to faster flood-water drainage. The changes in land use due to direct deforestation of wetlands has led to loss in valuable resources as fishes, shell fish, fuel, fodder, medicine, honey and beeswax and chemicals for tanning leather (Mitchell Beazley, 1993). Besides these economic losses, changes in land-use result in accelerated water leading to soil erosion, siltation of river courses and wetland filling with entrained sediments. Further construction of canals and diversions of streams and rivers to transport water to lower arid regions for irrigation has altered the drainage pattern and significantly degraded the wetlands of the region. For instance, the Indira Gandhi Canal Project across the river Sutlej in Gujarat removes water from the river as it drains from the western Himalayan mountains and diverts it via a canal system to the desert region of the state and neighbouring Rajasthan providing irrigation to cash crops. This has led to changes in the physical and chemical conditions of the soil, ecological problems, invasion of exotic plant varieties, salinisation, regional desertification and elimination of culturally sustainable life styles. This has further led to overdrawing of water leading to groundwater depletion in the area to as much as 1.5-2.0 m. Soil erosion resulting from this change in hydrological conditions has indirectly eliminated many wetlands by filling them as observed in many parts of urban India. Over withdrawal of ground water has led to salinisation threatening to reduce the economic benefits the society can derive from wetlands. Cumulatively this altered hydrology can dramatically change the character, functions, values and appearance of wetlands in the region.

Agricultural activities

The conversion of wetlands, deltas and floodplains of most rivers in India to paddy fields is rampant, following 'Green revolution' of the early 70’s. It is an ecological irony that as a result of this, the gross spatial extent of wetlands in the Indian subcontinent is greater today than it was 3000 years ago (Lee Foote et al., 1996) owing to increased paddy fields treated as wetlands. The rich Gangetic floodplains, with easy access to water, constitute one of the most intensively cultivated regions of the world and Kolleru lake in Andhra Pradesh has lost some 34,000 hectares of natural wetlands to agriculture (Anon, 1993). This was followed by profound changes in the irrigation pattern in India. The irrigated land increased from 3044 km2  (in 1970) to 4550 km2 (in 1990), showing 49% increase in the area (Anon, 1994). The demand for water to irrigate crops has increased dramatically over the last few decades resulting in the construction of a large number of reservoirs, canals and dams significantly altering the hydrology of the associated wetlands. In India, currently there are more than 1,500 large reservoirs covering 1.45 million hectares and more than 100,000 small and medium reservoirs covering 1.1 million hectares (Gopal, 1994). Reservoir construction has to a certain extent helped in justifying the beneficial effects in terms of economic benefits, especially

The fishing communities and farmers in the vicinity. But these impounding waters also significantly alter the catchments causing long-term costs in terms of ecological and social impacts (which are often overlooked in most of the hydrological projects). This kind of adhoc planning strategies do have serious environmental and ecological consequences which is evident from development activities in Saurashtra region, where over exploitation of ground water has led to steep fall in the water levels (up to 1.5 to 2.0 m per year) and also to salinisation (Lee Foote et al, 1996).

 The demand for shrimps and fishes has provided economic incentives to convert wetlands and mangrove forests to develop pisciculture and aquaculture ponds (Jhingran, 1982). Both rice fields and fishponds come under wetlands and seldom function as natural wetlands. However, such systems greatly alter the resident biota by altering the flow of detritus and soluble soil nutrients that initiate the food web, hampering ecosystem equilibrium.


The degradation of water quality is a direct consequence of population growth, urbanisation and industrialisation. Unrestricted dumping of sewage with toxic chemicals has polluted many freshwater wetlands, making them unfit for drinking, fishing or bathing in most parts of India. According to the study conducted by Chopra (1985), more than 50,000 small and large lakes in India are polluted to the point of being considered ‘dead’. The natural coastal wetlands are also polluted to the extent that their fishery and recreational values are lost. The prime sources of pollution are domestic and industrial sewage as point source besides agricultural runoff and the more insidious atmospheric pollution contributing to the non-point source pollution. Studies suggest that 70% of the 3,100 cities and towns (population >100,000) in India have no sewage treatment facilities (Gopal, 1994).

 Legal-policy failures

Wetlands jurisdiction is diffused and falls under various departments like agriculture, fisheries, irrigation, revenue, tourism, water resources and local bodies. For instance, all mangroves in the country fall under the direct control of forest department. The lack of a comprehensive wetland policy, with each department having its own developmental priorities, works against the interests of conservation of wetlands resulting in intended or unintended 'spill-over' further aggravating the problem. For example, the various subsidies and cross-subsidies given to irrigation, fertilizers - pesticides, land use policies, etc., have negative impact on wetlands. The divergence of wetlands and its benefits between the private and social, and lack of awareness in appreciating the full economic benefits on the part of policy makers have led to its market failure. At policy level, wetlands are too often taken for granted and are considered as wastelands and targeted for development to other immediate uses. A survey conducted by WWF-IUCN covering some of the important wetlands in India identified wildlife poaching (38%), pollution (37%), grazing pressure, alteration to other land uses, over-fishing and siltation as some of the major threats. The developmental policies of the government encourage large-scale aquaculture, pisciculture and salt manufacturing as in Chilka lake and west coast mangroves or pisciculture in Kolleru lake.

 Direct deforestation in wetlands

Mangroves are specialised, flooding and salt-tolerant shrubs and trees that grow along the coasts in the tropics. In India, mangrove forests are valued for production of fish and shell-fish, live-stock fodder, fuel and building materials, local medicine, honey and bees-wax and for extracting chemicals used in tanning leather (Ahmad, 1980). Alternative land-uses of farming and fisheries production have replaced many mangrove areas and continue to pose threats to the forests. The loss of wetland forests, coastal or riverine, reduces the ability of wetlands to slow water and trap suspended sediments.

 Inundation by dammed reservoirs

There are currently more than 1550 large reservoirs covering more than 1.45 million ha, and more than 100,000 small and medium reservoirs covering 1.1 million ha in India (Gopal, 1994). Due to erratic alterations of impounded water levels, the potential for shoreline wetlands to develop and mitigate the losses of river bottom and riparian zones is minimal. As a result of variable dam releases for power generation, the wetted area does not follow a predictable seasonal pattern, precluding development of a stable wetland flora and wildlife community.

Degradation of water quality

More than 50,000 small and large Indian lakes are polluted to the point of being considered ‘dead’ (Chopra-1985). The primary sources of pollution are human sewage, industrial pollution and agricultural runoff that may contain pesticides, fertilisers and herbicides. Pollution of lakes makes the water unsuitable for drinking, fishing or bathing. Extreme organic pollution levels from sewage can be put to constructive use in some situations. But, the unrestricted dumping of industrial wastes into the sewage stream threatens this situation. India’s wetlands have been given a respite in terms of agricultural runoff.

 Global climate change effects

Wetlands both contribute to and suffer from climate change. They are the single largest source of methane; a gas that is a major contributor to the atmospheric trapping of heat which leads to global warming. Unlike most regions of the world, the population of India has been high enough to cause change in the landscape. Continued degradation of water and wetland resources means that extensive regions will be marginalized or rendered less habitable by people and domestic animals if a warming and drying cycle of change affects India’s climate.

 Ground-water depletion

Demand for water to irrigate crops has increased dramatically in the last 20 years. Between 1980 and 1983 the rapid depletion of ground-water left over 60,000 villages in rural India with no source of drinking water (Chopra 1985). Water pumping continues to reduce ground-water level by 1.5 to 6 m per year in some areas, and the beds of rivers that once flowed continuously are now dry for much of the year.

 Introduced species - extinction of native biota

Indian wetlands are threatened by exotic plant species such as water hyacinth and salvinia. These free-floating nuisance plants were introduced in India and pose problems by clogging waterways and competing with native vegetation. As habitats are changed, exotic plants may be favoured over native plants. When wetlands lose native species of animals and plants, they are thought to be of lower value making it harder to justify their defence.  


Karnataka is situated between 11o 31 and 18o 45’ north latitudes and 74o 12’ and 78o 40’ east longitudes. It is blessed with numerous rivers, lakes and streams. Its length (north to south) is about 750 km and width (from east to west) about 400 km. The state covers an area of 1,92,204 sq. km, which is 5.35 % of the total geographical area of the country, with a coastline of about 320 km. There are nineteen districts in the state. The provisional population of Karnataka after the conclusion of 2001 census is a little over 52.7 million, of which, males accounted for 26.8 million while the female population was 25.8 million (Shashidhar, H, 2001). In 1991, of the total population of 44.9 million, males were 22.9 million and females 22 million (Rege, et al., 1996). The state now ranks ninth in population size and shares 5.13 per cent of the country's total population (Shashidhar, H, 2001).

 Southwest and northeast monsoons contribute to a major portion of the rainfall. Annual rainfall varies from 3932.9 mm (Dakshina Kannada) to 142.4 mm (Bijapur). There is also negligible quantity of rainfall during summer and winter. Temperature is lowest in early January, increasing gradually at first and rapidly after mid-February to early March. The warmest month in major parts of the state is May when maximum temperature is recorded. It reaches 43°C in Gulbarga - Raichur region. In Bidar, Gadag and Bellary, it exceeds 40°C. In the coastal area it is about 35°C to 36°C. Over the southern maidan, it is about 36°C to 38°C. It is 32°C to 34°C in the Western Ghats and Malnad area.

 Distribution of wetlands

Wetlands of Karnataka are classified into inland and coastal wetlands, both natural and man-made. Inland natural wetlands include lakes, ox-bow lake and marsh/swamp; inland man-made wetlands include reservoirs, tanks, and waterlogged plains. Coastal-natural wetlands include estuary, creek, kayal, mudflat, mangroves and marsh vegetation; coastal man-made wetlands include saltpans. Wetlands cover about 2.72 Mha of the total geographical area of Karnataka, of which inland wetlands cover 2.54 Mha and coastal wetlands 0.18 Mha.

 Totally, 682 wetlands are scattered throughout Karnataka covering about 271840 ha. Out of these, seven wetlands are inland natural (581.25 ha), 615 inland man-made (253433.75 ha), 56 coastal natural (16643.75 ha) and four coastal man-made (1181.75 ha). The inland wetlands cover 93.43 % (254015 ha) of the total wetland area, while coastal wetlands cover only 6.57 % (17825.5 ha). Tanks (561) rank first in the number of wetlands and account for 79087.50 ha. Reservoirs come next in number (53) with an area of about 174290 ha. Lakes are fewer in number (5) covering 437.5 ha. Mangroves in Karnataka cover 550 ha. Karnataka has the basins of Krishna (58.9 %), Cauvery (18.8%), Godavari (2.31%), North Pennar (3.62 %), South Pennar (1.96%), Palar (1.55 %) and west flowing rivers (12.8%) draining 1,91,770 sq. km (Rege, S.N et al, 1996). As per 1996 statistics, there were nineteen districts in the state and wetlands distributed in different proportions in all of them. Table 6 gives the district-wise distribution of wetlands (Rege, et al, 1996).

 Table 6: District–wise distribution of wetlands in Karnataka

Wetland Type  


Oxbow lake Swamp / Marsh Reservoirs Tanks Estuary Manrovesg Salt marsh /pans Others No Total area(ha)
Bangalore - - 2 48 - - - - 50 10512
Belgaum - - 3 8 - - - - 11 19733.25
Bellary - - 4 35 - - - - 39 35300
Bidar - 1 1 2 - - - - 5 887.50
Bijapur - - 4 25 - - - - 29 12993.75
Chick-magalur - - 1 15 - - - - 16 19775.5
Chitradurga - - 4 51 - - - - 55 13087.50
Kodagu - - 1 -- - - - - 1 462.50
Dharwad - - 1 35 - - - - 36 4400
Gulbarga - 1 5 21 - - - - 27 4625
Hassan - - 2 29 - - - - 29 9843.75
Kolar - - -- 58 - - - - 58 1029.4
Mandya - - -- 25 - - - - 27 3312.5
Mysore - - 6 49 - - - - 56 26450.6
Uttara Kannada - - 3 2 4 2 9 14 34 28131.25
Raichur - - 1 27 - - - - 29 3099.5
Shimoga - - 11 10 - - - - 21 45756.75
Dakshina Kannada - - -- -- 7 5 1 13 27 4375.00
Tumkur - - 4 121 - - - - 125 18249.5


Deforestation and other anthropogenic activities have accelerated soil erosion causing increased sedimentation resulting in shrinkage of area under wetlands. Some reservoirs and other waterbodies in Karnataka are facing the problem of siltation. The number of wetlands in Karnataka has halved during the last century.


It is a significant parameter in determining the opaqueness of water that helps photosynthetic processes and fish life. It mainly depends on particulate matter present in the water. Wetlands in Karnataka are classified in to low, medium and high based on the turbidity values. Among 620 surveyed wetlands, about 200 wetlands have low turbidity, 222 moderate and 198 high turbidity. Under the wetland categories, tanks (161) have the lowest turbidity, followed by reservoirs (36), lakes/ponds (2) and ox-bow lakes (1). Under moderate classification, tanks (212) again rate first followed by reservoirs (9) and lakes (1). Nearly 188 tanks have high turbidity followed by reservoirs (8) and lakes (2).

 Aquatic vegetation status 

Wetlands usually support diverse aquatic vegetation. Aquatic weeds are generally used as indicators of eutrophication. These are ideal habitats for fish and migratory birds. On the basis of vegetation, Karnataka is divided into four zones namely completely vegetated (CV), partially vegetated (PV), vegetation on fringes (VF) and no vegetation (NV). Of the 682 wetlands in Karnataka, 517 do not have vegetation, out of which 417 are tanks. Eighty-three tanks show partially vegetated condition, 54 have vegetation on fringes and 7 are completely vegetated.

 Seasonal variation in water spread of wetlands

The total water spread area in pre-monsoon is 204053.74 ha while in post monsoon it is 246643.00 ha. Out of 682 wetlands in the state, 71 have shown water spread less than 56.25 ha (Rege, S.N et al 1996). The water-spread area of lakes/ponds in post monsoon is about 437.50 ha while in pre monsoon it is about 368.75 ha. Reservoirs have shown considerable variations from post monsoon (167268 ha) to pre monsoon (138684.25 ha). Tanks also vary from 46975.25 ha in post monsoon to 60912.25 ha in pre monsoon. The coastal wetlands, which are under constant influence of the sea have not shown any variations and remained unchanged in terms of water spread area in all seasons. Most of the tanks dry up during pre-monsoon seasons.

 Wetlands of Karnataka have already been lost in the process of urban development and over population. The peripheral areas of wetlands in the state have been encroached for settlements. A large number of wetlands in the state are subjected to inflows of domestic sewage, solid waste and industrial effluents, responsible for decline in their quantity and quality. Fertiliser and pesticide run-off from agricultural lands has also aggravated the pollution load. These threats have degraded species diversity and the productivity of the wetlands.


Bangalore district is located in the heart of South Deccan of Peninsular India. It is situated in the south-eastern corner of Karnataka state (12o39 – 13o18N latitude and 77o22 – 77o52 E longitude) with a geographical area of about 2,191 sq. km and an average elevation of 900 m above the mean sea level. The climate of the district enjoys an agreeable temperature range from the highest mean maximum of 36.2o C in April to lowest mean maximum of 11.4o C in January. It has two rainy seasons from June to September and from October to November coming one after the other but with opposite wind regime, corresponding to south-west and north-east monsoons. The mean value of the rainfall of about 900-mm with standard deviation of 18.7 mm was recorded from the year 1875 to 1976 (Srinivasa et al, 1996).

 Bangalore city once sported a large number of lakes, ponds and marshy wetlands, which ensured a high level of ground water table and pleasant climate. It is a great pity that many lakes and ponds have already disappeared due to various anthropogenic activities and pressures due to unplanned urbanisation and expansion. Surviving lakes are reduced to cesspools due to direct discharge of industrial effluents and unregulated dumping of solid wastes.


Wetlands of Bangalore occupy about 4.8% of the city’s geographical area (640 sq km) covering both urban and rural areas (Krishna et al., 1996). Bangalore has many man-made wetlands but no natural wetlands. They were built for various hydrological purposes to serve the needs of irrigated agriculture. Totally there were 262 lakes coming within the green belt area of Bangalore City. Bangalore Metropolitan Area is divided into 7 taluks.  Table 7 gives the distribution of tanks by taluks in Bangalore (Chakrapani, 1996).

  Table 7: Distribution of tanks by taluks

Sl. No Name of the Taluk No. of tanks
1 Bangalore North 61
2 Bangalore South 98
3 Hoskote 23
4 Anekal 44
5 Magadi 11
6 Nelamangala 13
7 Devanahalli 12

 The number of tanks in Bangalore has fallen from 262 in 1960 to 81 at present (Lakshman Rau, 1986). These 81 lakes have been classified in to four categories depending on the spatial extent (Table 8). 

Table 8: Distribution of 81 live lakes based on area

Area No. of lakes
Area < 10 ha 49
Area between 11 and 20 ha 16
Area between 21 and 50 ha 14
Area > 50 ha 2
Total 81

Table 9: Spatial extent of some 17 existing lakes

Sl No Lake Area  (ha)
1 Vasanthapura 2.0
2 Dorekere 11.29
3 Moggekere 6.06
4 Madivala 114.20
5 Agaram 56.67
6 Puttenahalli 32.89
7 Doddabegur 32.86
8 Ulsoor 49.80
9 Bellandur 361.30
10 Narasipura-1 3.62
11 Narasipura-2 6.12
12 Doddabommasandra 40.90
13 Nagavara 22.46
14 Lalbagh 96.00
15 Kempambudhi 14.84
16 Hebbal 76.87
17 Hulimavu 49.70
  TOTAL 977.58


Status of wetlands in Bangalore is a direct measure of status of management of anthropogenic activities, management of land, solid waste collection and disposal, disposal of used water and also attitude of the people at large. In Bangalore wetlands are being lost due to:

 q      Anthropogenic stress.

q       Increasing population and growing economy leading to unplanned urban development that has put greater pressure on the land resources.

q      Lack of governmental commitment, cohesive academic research on wetland in understanding the importance and essence of conservation and management owing to financial constraints and lack of infrastructure and required expertise.

q       Deficiency in proper management of non point source of pollution like storm water and agricultural runoff, and unregulated land use management have also led to the steady increase in problems of pollution, eutrophication, invasion of exotic species, toxic contamination by heavy metals, pesticides and organic compounds (Kiran, R and Ramachandra, T.V, 1999).

  The lakes are unique features of the ecology of the city. Bangalore supports no natural wetlands, the present one’s were built mainly for various hydrological purposes and to serve the needs of irrigation and drinking water supply. The vast majority of the wetlands in Bangalore occur on the outskirts of the city, in the rural fringe. Studies on lakes of Bangalore during the past decade, show that 35% tanks were lost owing to various anthropogenic pressures. Converting wetlands for residential, commercial and agricultural purposes has also been a part of the mosquito eradication program of the Bangalore Development Authority (Deepa et al., 1997). Remaining lakes are dying fast, as they are filled with solid waste materials and sewage. The present trends in decrease in the water quality and number of water bodies are the result of unplanned development of the city, resulting in vast tracts of wetlands being cleared. Recent studies on lakes of Bangalore show that nearly 40 % of lakes are sewage fed, 13 % surrounded by slums and 35% showed loss of catchment area. The major problems of the city’s tanks are lack of government records and sewerage entering them (65 are sewage fed, 16 are breached). Lakes situated outside the city’s limit face the problem of brick kiln contributing to the declining water quality.

 The number of man-made wetlands has fallen from 379 in 1973 to 246 in 1996 and further reduced to 81 at present (Lakshman Rau, N et al., 1986). About 133 water bodies have been lost in North (42) and South (91) taluks during a period of two decades. Table 10 gives the percentage loss of number of tanks in North and South taluks (Kiran.R and Ramachandra T.V, 1999).  

Table 10: Region-wise spatial extent and status of tanks

Region Area in sq. km No. tanks (1973) No. tanks (1996) Percentage loss (No. of tanks)
North 506.87 138 96 30.43
South 594.96 241 150 37.75
Total 1101. 8 379 246 34.09

Earlier investigations have revealed that nearly 30 % of lakes are used for irrigation. Fishing is being carried out in 25 % of the lakes surveyed. About 36 % of lakes are used for washing purposes and only 3% are used for drinking. Agriculture along the margins is practiced in 21% of the lakes. Approximately 35% of lakes are used for grazing by cattle. Mud lifting was recorded in 30 % of the lakes and brick making in 38 % of the lakes (Srinivasa, 1996). 

      ·        Lake structure status - As the city expands, more and more lakes are being walled up to restrict the water spread.

 ·         Water level status – The level of water in wetlands or any water body is significant in determining the waterfowl population and diversity. Nearly 23% of lakes were dry due to lack of rains in the past two years while 25% had little water (Srinivasa, 1996).

 ·         Status of lakes due to sewage and effluents – The presence of sewage and varied degree of eutrophication were recorded from 28% of lakes in 1996, while it was about 10% in 1989, 13% in 1992 and 16 % in 1995. About 25% of lakes (1996) have suffered from green waters as compared to 8% in 1989. Approximately 8 % of the lakes had other effluents. It is disheartening to see that nearly 30% of vegetables are grown with these untreated waters (Srinivasa, 1996).

 ·         Encroachment and reclamation status - Nearly 30% of the lakes was encroached for mud lifting and 38% for brick making processes. About 30% of the lakes were drained either for residential sectors in their ornamental borders or converted to layouts. Nearly 22% of the lakes were encroached for agricultural purposes, slums surround 13% of the lakes and unauthorised buildings (Srinivasa, 1996). In some cases, land filling and walling of the lake margin has been observed. For instance, Miller tank was converted into a housing layout, Shulay tank was filled up and a football stadium constructed, Akkithimmanahalli tank near Langford road was converted in to a housing layout with a hockey stadium built on the site and the Domlur tank converted into a BDA layout. Sampangi tank has given way for the construction of a sports stadium and the corporation now maintains a small replica of this tank in the grounds.

 ·         Poaching of birds and species diversity - Water birds, in particular larger ones like ducks, geese, storks, ibises and cormorants are hunted to a large extent. Poaching of water birds increases during October and April. Poaching was recorded in eight lakes, which increased from 7.5 % of total area in 1996 while the corresponding amount in 1989 was about 35%. Reduction in the percentage has occurred mainly due to the fact that the number of dry lakes in 1996 was much more than in 1989 (Krishna, et al., 1996). Over 330 species of birds have been recorded in Bangalore. Out of these nearly 40% occur in or near wetlands. These represent 19 different families. Nearly 91,000 birds were identified in 1996 as compared to about 52,000 birds in 1995 (Krishna, 1996).

·         Phytoplankton and Zooplankton diversity - Microcystis species accounted for about 68%, and Phormidium species 55% of the lakes. Aphanizomenon, Anabaena, Oscillotaria, Spirulina Coelosphaerium, Nostoc and Lyngbya species were also recorded during the two surveys of lakes in and around Bangalore. Totally 72 lakes were surveyed in 1989 and about 56 phytoplankton forms were observed. But within 6 years, the number of phytoplankton forms had increased to 66 including 8 unidentified forms in 60 lakes (Chakrapani, 1996). Totally, 62 forms of zooplankton including 5 unidentified forms were recorded during the survey of 1995, which was less in number (54 forms with about 9 unidentified forms) when compared to the survey of 1989 (Chakrapani, 1996).

 ·         Quality status - The colour of the polluted waterbodies was mostly greenish indicating eutrophication mainly due to algal blooms followed by the contribution of effluents from domestic and industrial sources. Nearly 23% of lakes are suffering from eutrophication due to inflow of sewage (Chakrapani, et al, 1996).

 The pollution has resulted in "significant degradation" to the aquatic ecosystem evident from frequent fish kills (Benjamin et al, 1996) with significant adverse effects on:

      1)    Human health or welfare, including effects on municipal water supplies as noticed in few tanks as Kamakshipalya              and Kempambudhi tanks.

2)       Life stages of aquatic life and other life forms dependent on aquatic ecosystems, such as decreased population of birds (Krishna al, 1996), fish, etc.

3)       Ecosystem diversity, productivity and stability, including loss of fish and wildlife habitat or loss of the capacity of a wetland to assimilate nutrients, purify water, etc., and

4)    Recreational, aesthetic, and economic values.

 The disappearance of the tanks which play a vital role in the microclimate of the region, especially during summer, mitigating the heat, has reflected changes in terms of the air, water and ground water quality, and rainfall and temperature patterns of the city.

 §         Turbidity in the cleaner waterbodies ranged from 1.0-25.0 NTU (Nephlometeric Turbidity Units) and 70.0-362.0 NTU in polluted waterbodies, primarily due to silt, suspended and organic matter and autochthonous sources (mainly planktons). The sources are mainly the stormwater and agricultural runoff, and effluents from industrial and domestic sectors, which in turn restrict the penetration of light, giving rise to reduced photosynthesis and aesthetically unsatisfactory odours (Kiran, R and Ramachandra, T.V, 1999).

 §         The pH values ranged from 7-9.3 in urban areas and 7.3-8.7 in non-urban areas. Kamakshipalya recorded 6.0 - 6.6 during the entire study period (Kiran et al, 1999). pH values above 9 (alkaline) were recorded at Yediur, Puttenahalli and Ulsoor tanks (Chakrapani, et al., 1996).

 §         The COD values ranged from 27 mg/L in unpolluted waters to a high of 621 mg/L in Kamakshipalya, as a result of pollution that is largely determined by the various organic and inorganic materials [calcium, magnesium, potassium, sodium etc] (Kiran, R and Ramachandra, T.V 1999).

 §         The dissolved oxygen concentration of the analysed waterbodies ranged from 1.2 mg/L in Kamakshipalya lake to 11.1 mg/L in Ulsoor and Yediur lakes largely due to photosynthetic activity (Kiran et al., 1999). The recommended dissolved oxygen concentration for a healthy and ideally productive lake waterbody is 8 mg/L (Wetzel, 1973).

 §         The level of phosphates was found to range from 0.06 mg/L to a high of 4.2 mg/L, the higher values were seen in Kamakshipalya lake (Kiran, R and Ramachandra, T.V, 1999). Phosphates have the tendency to be precipitated by many cations and accumulate at the bottom of the lake becoming temporarily inaccessible to productive organisms.  The nitrate concentration was found to range from 0.1 to a very high level of 2.7 mg/L in view of the standard level for inland surface water fixed at 0.1 mg/L (NEERI, 1988). This parameter is very significant in relation to algal productivity (algal blooms) in lakes, which mainly leads to eutrophic condition (Kiran, R and Ramachandra, T.V 1999).

 §         Dissolved solids ranged from 30-301 mg/L in less polluted lakes like Bannergatta and Sankey and 430.0-1024.0 mg/L in highly polluted lakes such as Kamakshipalya and Yediur. The suspended solids ranged from 52.2 mg/L to a high of 278.3 mg/L as a result of silt and suspended nutrients (Kiran, R and Ramachandra, T.V, 1999).

 §         Among the heavy metals, iron and lead were present in higher quantities and the other two parameters zinc and chromium were in traces (Kiran et al, 1999). The permissible limit for iron is 0.3 mg/L (NEERI, 1988) for drinking water. Above this value, iron imparts bitter astringent taste (Chakrapani et al, 1996).

Investigations revealed that most of the analysed parameters for the lakes in Bangalore (e.g. Ulsoor, Hebbal, Yediur, Kamakshipalya and Madivala) exceeded the limits set by Indian Standards for industrial and sewage effluents discharge [IS 2490 -1982] (Kiran and Ramachandra, T.V, 1998).

Preface                                                                                                                                   Methodology