Cernek Lake is one of the most valuable wetlands of Northern Turkey. The lake and the surrounding wetlands are characterized by a high degree of biodiversity with reference to the species and natural habitats, so it has been recognized as a "Ramsar Site". The lake is a typical shallow lagoon lake, which is subjected to human activities such as discharge of sewage. In order to evaluate the biotic community and estimate the pollution level, the physical and chemical variables and plankton dynamics were investigated during the study period. The plankton composition was typical for an eutrophic ecosystem. Cyanophyta and Chlorophyta. mainly were the dominant algal assemblages in terms of abundance. The zooplankton community was dominated by Rotifers (Brachionus and Keratella), whereas small Cladocera (Chydorus sphaericus and Bosmina longirostris) was also important in fall months. Primary production ranged between 569 and 4303 mg C m(-2) day(-1), while chlorophyll a ranged between 4.12 and 541.5 mg m(-3). The chlorophyll a content indicated also that the lake was eutrophic with hypertrophic tendency.