Lake Vendyurskoe, located in central Karelia, is a small mesotrophic reservoir typical of Fennoscandia. A trout farm has been operating there for 12 years. In addition, in recent decades, an increase in the variability of the regional climate and a change in the timing of the main hydrological phenomena have been noted. It is important to study the response of zooplankton to changes in environmental conditions. The species composition of pelagic zooplankton and the conditions in its habitats were studied in different seasons of 2020 and 2021. According to our data, 41 taxa with genus rank and lower were found in the lake. The number of species varied among seasons from 12-13 in the end of the ice period to 29 in summer. No effect of the trout farm on the species composition of zooplankton in Lake Vendyurskoe has been revealed. In the fall of 2020, an alien species - American rotifer Kellicottia bostoniensis (Rousselet, 1908), was first discovered in the lake, remaining present until the spring of 2021. This is the first time this rotifer has been discovered in Karelia during the ice-covered period. A noticeable development of the alien species may indicate the conditions in its habitat have become favorable. At present, the overall species list of zooplankton of Lake Vendyurskoe, taking into account the results of previous studies, comprises 92 species (rotifers - 27, copepods - 24, and cladocerans - 41). Most of it (more than 80 %) is oligotrophic and oligotrophic-ß-mesotrophic species.