Abstract: The algae in Taipinghu Reservoir and its trophic level were investigated during 1985—1986. 175 species of algae are observed. Chlorophyta is the most important group with 87 taxa, representing50% of the total. Bacillariophyta and Cyanophyta are subdominant groups with 34(19.4%) and 33(18.8%) taxa respectively. Other five phyla with 21 taxa are less important, representing11.8% of the algal flora. According to the results of trophic evaluation, this reservoir is a mesotrophic waters with clear water. Two parameters (dominant species and TN) achieve eutrophic level, and the blooms of Microcystis occurred sometimes indicate that the trophic level of the reservoir is transiting from mesotrophy to eutrophy. At present, the overgrowth of algae is limited by low phosphorus concentration (TN 0.012mg/L). In order to avoid further eutrophication, it is important to prohibit the discharge of phosphorus and nitrogenous compound into the reservoir.

Key words: Reservoir, Algae, Biomass, Seasonal change, Trophic level