Species richness and spatial heterogeneity of spring phyto- and zooplankton were studied in a slightly eutrophic lake. Plankton of one meter below the water surface was compared in the main basin of the lake, a shallow, small basin, and a bay of intermediate depth. The results suggest that the two shallower sampling stations lifted up the lake phytoplankton species richness considerably, whereas no such effect was noted for the zooplankton. There were differences between the three sampling stations in dominant taxa, as well as in the abundance and biomass of both phyto- and zooplankton.