Between June 1999 and May 2000, the epipelic algal flora and its seasonal variations in the River Ye¸silırmak were investigated.A total of 69 species were identified, most of which belonged to the Bacillariophyta. Other taxonomic groups present were Chlorophyta, Cyanoprokaryota and Euglenophyta. Pennate diatoms, especially Nitzschia palea, Navicula cincta, N. cryptocephala, Amphora ovalis and Fragilaria ulna, were the most abundant species, with species of centric diatoms found in lower numbers. Cyanoprokaryotes (Cylindrospermum stagnale and Oscillatoria spp.) and Euglenophytes (Euglena deses f. major and E. satelles) were also common. The epipelic algal flora and its seasonal variations were similiar at all stations, with the greatest number of species observed in July, September and October. A decrease in the number of algae due to rainfall was observed at all stations. Cluster analysis was applied to the epipelic algal community.