The primary production of littoral algae was characterized by periodical high intensity, with a maximum in summer (0.204 g C m-2 24 h-1 phytobenthos and 2.77 g C m-2 24 h-1 phytoplankton). The investigation results support the hypothesis that in certain environmental conditions, besides ecological competition between the algae, the phytobenthos and phytoplankton communities are mutually enriched with species. The more labile phytoplankton communities, however, have a greater effect on the quality of the water in the studied reservoir than have the communities of phytobenthos.