belonging to the phylum Heterokontophyta, and cy-anophytes (34). Chrysophyceae and Xanthophyceae were the least common among the representatives of the lake phytoplankton. In Lake Œlesiñskie at least 240 taxa were recognized (Table 2), with the most taxarepresentedbygreenalgae(127),andthefewest among cryptophytes and euglenophytes (Table 2). The frequency structure of the phytoplanktontaxa in the two lakes differed, and in both lakes themajority of taxa had frequencies of less than 25%. InLake Licheñskie the number of taxa in subsequent groups on the Tichler scale decreased significantly (Table 3), while in Lake Œlesiñskie these changes were less pronounced (Table 4). The most taxaamong the incidental species belonged to the greenalgae and diatom groups. All of the euglenophytetaxa occurred at frequencies not exceeding 50%, while those of the cryptophytes occurred in excess of 50%