Abstract
U was demonstrated that the fungi decomposing protein were most abundant in tbe mesotrophic lake, whereas the fungi decomposing pectin dominated in the eutrophic lake. The accumulation of fungi mineralizing protein in littoral zone (metha- and hypolimnion of pelagial zone) of the mesotropbic lake indicated the increase in the fertility of this reservoir. The frequency of occurrence of physiologically differentiated mycoflora in the lake waters was seasonal and revealed fluctuations in their activity depending on the year of the study. These fluctuations were stronger in the mesotrophic lake.