Abstract: A total of 19 investigations were conducted on the phytoplankton community structure and water quality in Shuifeng Reservoir during June 2010 to October 2019. A total of 76 phytoplankton species (abundance >1000 cells·L^-1) were recorded, which belonged to 7 phyla and 43 genera. There were 33 species of Bacillariophyta, 27 species of Chlorophyta, 6 species of Cyanophyta, 5 species of Euglenophyta, 2 species of Cryptophyta, and 1 species of Pyrrophyta. The abundance of phytoplankton was 1.20×10⁴-6.03×10⁶ cells·L^-1, with an average of 7.13×10⁵ cells·L^-1. The dominant species were Aphanizomenon issatschenkoi, Dinobryon divergens, Melosira granulata, Cyclotella meneghiniana, Cyclotella comta, Fragilaria crotonensis, Synedra acus var.angustissima, Asterionella formosa, Mougeotia sp., and Closterium acicular var. subprorum. Indicated from the dominant species, pollution-indicating species, abundance of phytoplankton, Shannon diversity index and trophic level index, Shuifeng Reservoir was at a mesotrophic state or mesotrophic-eutrophic state. The comprehensive index of algae indicated that Shuifeng Reservoir was at a eutrophic state. The biomass of phytoplankton indicated that Shuifeng Reservoir was at an oligotrophic state. Taken together, the Shuifeng Reservoir was at the mesotrophic state.

Key words: Shuifeng Reservoir, eutrophication, biological diversity, trophic state.