Abstract: 【Objective】Analyze the species,density,biomass,diversity and other community characteristics of plankton in combination with the assess of dominant plankton and water quality physical and chemical indicators to evaluate the water quality of Juyan Lake. 【Methods】From November 2020 to September 2021,13 physical and chemical indicators of water quality as well as plankton resources in the Juyan Lake were sampled and analyzed in accordance with Handbook of Fishery Natural Resources Investigation in Inland Waters and Technical Specification for Freshwater Plankton Investigation（SC/T 9402—2010）. 【Results】 In the survey duration,the transparency of Juyan Lake water body was 0.45-1.08 m,the total nitrogen was 0.97-2.48 mg/L,and the total phosphorus and nitrogen nutritional status indices were 33.79-35.09 and 54.01-69.92 respectively. 6 phyla and 63 species of phytoplankton were identified,including 16 dominant species with densities of 236 500 to 392 600 per liter,biomass of 0.30 to 1.04 mg/L,Shannon-Wiener diversity index of 2.53 to 2.88 and the richness indices of 2.64 to 3.08. 2 phyla and 22 species of zooplankton were identified,including 17 dominant species,with densities of 35.98 to 131.95 per liter,biomass of 0.27 to 1.12 mg/L,Shannon-Wiener diversity index of 2.80 to 3.23,and the richness indices of 2.35 to 2.93. Two species of α-polysaprobic zone indicator organisms and two species of β-polysaprobic zone indicator organisms,nine species of α-mesosaprobic zone indicator organisms and eight species of β-mesosaprobic zone indicator organisms and two species of oligosaprobic zone indicator organisms were detected.【Conclusion】The physical and chemical indicators of Juyan Lake revealed that the water body was in eutrophic state,mainly manifested as nitrogen levels far over the standard. Plankton biomass showed that Juyan Lake′s water was in oligotrophic state. The density of phytoplankton indicated that the aquatic body was in oligotrophic to mesotrophic state. Dominating plankton species,pollution indicator organisms,and Shannon-Wiener diversity index all showed that Juyan Lake was in mesotrophic or medium eutrophic state. Comprehensive analysis revealed that Juyan Lake′s water quality was mesotrophic.

Key words: Juyan Lake, Plankton, Community characteristics, Water quality evaluation