The biological examination of the stream and reservoir ecosystems of Sharavathi River basin showed a rich and diverse phytoplankton population. Desmids predominated in reservoir waters while diatoms in streams. Species diversity is not uniform either in streams or reservoir waters. From various pollution indices, it is clear that the waters of reservoir are in oligotrophic nature, even though the streams showed slight organic pollution. The study emphasises the requirement of proper conservation of phytoplankton-the primary producers, on which most of the higher aquatic organisms are dependent.