The predatory impact of Leptodora kindtii on the zooplankton community of Slapy Reservoir (Czech Republic) was studied using data from regular sampling carried out in 1996-1997. Seasonal changes of abundance and biomass of Leptodora, that directly influence predatory impact, were analyzed and related to both abiotic and biotic parameters. The data suggest that Leptodora can influence the zooplankton community, but only in limited periods during the summer season, with the most pronounced impact in August. Leptodora can apparently accelerate the summer decline of spring cladoceran species, although it does not trigger the shift to summer species.