The seasonal variations in composition and density of benthic algae of Karanlik Lake, and diversity of epipelic algae, have been investigated in 2001 and 2002. A total of 86 taxa were determined, and Cymbella minuta, Pinnularia maior and Surirella splendida were the most conspicuous algae, regarding frequency of occurrence and relative abundance in the benthic algal flora. While the highest density of the epipelic community was found to be 12079 cells/cm(2) at station I in October 2001, the lowest density was 5911 cells/ cm(2) at station II in September 2002. The highest Shannon-Weaver diversity index (H-1) in the epipelic flora was found to be 2.979 at station I in July 2002. Considerable differences were observed between the two stations in the seasonal fluctuations of total cell numbers and diversity index. In this study, ice, light and water temperatures were found to be more important factors in regulating the growth of benthic algal flora in Karanlik Lake, which is according with that of oligotrophic high mountain lakes of the Northern hemisphere.