The study was carried out in Vamanapuram River, Thiruvananthapuram district, Kerala, India to assess the water quality for domestic purposes between February and July, 2017. Fifteen physico-chemical parameters of water were estimated and qualitative and quantitative studies of algae were made. Low values of DO (3.0 - 3.97 mg/l) and high BOD (12.0 - 15.0 mg/l) indicate high level of organic pollution in the river. The water also contained high amount of TDS (297 – 733 mg/l) and phosphate (0.04 - 0.36 mg/l). The calculated water quality index value is 61.53 indicating its poor water quality. A total of 57 algal taxa were encountered from the river of which Ophiocytium parvulum(Perty) A. Br. and Triploceras gracile Bail var. elegans (Borge) Krieg. are reported for the first time from Kerala. The zooplanktons viz. Arcella arenaria, Difflugia sp. , Cyclopyxis plana and Centropyxis ecornis which are reported as indicators of organic pollution were abundant in the samples. Two algal pollution indices viz. Nygaard’s trophic state index and Palmers pollution index of Algal genera were employed to assess the level of organic pollution in the river. The values of both indices showed organic pollution in the river as it is also confirmed from the physico-chemical characters of water.

Keywords: Physico-chemical parameters, Phytoplankton, Protozoa, Water Quality index.