The studies conducted in the Gnieźnieńskie Lakeland in the summer seasons of 2001 and 2002 provided the basis for determining the abundance and species richness and diversity of zooplankton in the littoral zone of two lakes heated by waters discharged from power stations, and for describing the relationships between water thermal conditions and the density and structure of taxocoenoses. The effect of water temperature on the zooplankton was estimated using the Spearman rank correlation. Over the whole study period, the zooplankton in both water bodies exhibited a high species richness and a wide species diversity (expressed as the Pielou index) but a relatively low abundance and biomass. No significant relation was found between water temperature and the total abundance, biomass and diversity indices of zooplankton. On the other hand, there were significant relations between water temperature and the abundance and biomass of individual taxonomic groups.

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