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%. In