First ecological evaluation of the ancient Balkan Lake Megali Prespa based on plankton

The ecological water quality of one of the ancient world lakes, Lake Megali Prespa, is examined for the first time on the basis of its plankton communities. During the study period (October-November 2008) the lake's plankton showed signs of a moderate ecological water quality. This quality was reflected in: i) phyto-and zoo-plankton species composition which was characteristic of eutrophic conditions, ii) phytoplankton functional groups typical for eutrophic waters, iii) phytoplankton biovolume values, iv) the occurrence of blooms of several nanoplanktic species (cyanobacteria, diatoms, prymnesiophytes and cryptophytes) and v) the presence of known potentially toxin-producing cyanobacterial species. These plankton characteristics suggest a link to eutrophication and water quality degradation in the ancient Lake Megali Prespa. Water managers are advised to consider the data on plankton community and the species exchange between the lakes Megali and Mikri Prespa (high overlap of phyto- and zoo-plankton species) in their strategies for the conservation of this precious ancient lake of the world.