In recent research, the study of the quality of water and population of lake phytoplanktons in the Lake of Sanandaj Dam has been conducted for one year from June 2014 to June 2015. This study was carried out in 5 stations and 4 seasons, and identification of phytoplankton species was performed, and Shannon coefficient and Palmer coefficient were determined. In this study, six groups of phytoplankton Bacillariophyta, Chrysophyta, Pyrophyta, Cyanophyta, Chlorophyta and Euglenophyta were 20, 1, 9, 6, 16, and 2 species have been recorded in this study. Investigation of phytoplankton communities during the study period of the lake behind the Lake of Sanandaj Dam shows the dominant species of the Bacillariophyta group from diatoms with 20 species throughout the year, followed by a group of green algae or Chlorophyta with 16 species. The lowest frequency of species diversity was observed in Chrysophyta and Euglenophyta groups with 1 and 2 species, respectively. The Shannon index varied in different seasons, the highest in summer was 58.1 and then autumn (1.41), winter (1.24) and spring (1.19) respectively. The highest number of species belongs to the first station and the smallest of them belongs to the last station. The water quality of the Lake of Sanandaj Dam was studied through the Palmer biomarker. The final results showed that the quality of water in the Lake of Sanandaj Dam, except for some stations, is great quality.
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