The phytoplankton of Lake Simenit were studied from June 2000 to May 2001. A total of 167 taxa belonging to the Cyanophyta, Bacillariophyta, Chlorophyta, Cryptophyta, Dinophyta, Euglenophyta and Xanthophyta divisions were identified. Species belonging to the genera Chaetoceros, Cyclotella, Cocconeis, Scenedesmus, Anabaena, Euglena and Trachelomonas caused water blooms in certain months. The lake water was slightly alkaline and its hardness varied between hard and very hard. The water temperature and nutrient levels affected the composition of phytoplankton. Cluster analysis was applied to the phytoplankton composition. Stations were classified according to their similarity. The results of analysis support the results of the counting method.