The article presents results on the spatiotemporal variability of two zooplankton species – Daphnia cristata and Diaphanosoma brachyurum, in Lake Leschovoye. Surveys were conducted from June to September in 2016–2020. According to monitoring data from this period, the abundance of these species varied widely over time. Specific surveys at six sites in July–August 2019–2020 revealed also high spatial variation of the species’ abundances. Compared to the other species, D. cristata dominated in the lake with a 71 % share in Cladocera abundance. In 2020, however, D. brachyurum abundance was relatively high. In this period, its share in the cladoceran zooplankton reached 31 % and was twice that of D. cristata that year. A positive effect of water transparency on D. brachyurum abundance was observed. The study found no significant effect of other limnological parameters (gas conditions, pH, dissolved organic matter concentration, water color and turbidity) on the species. Another factor potentially influencing the species abundance is interspecific competition for food, as the range of particles consumed by the species is similar. Alongside competition, predation of plankton-feeding fishes and organic matter input with runoff from managed meadows can affect the abundance of the species. The effect of the runoff, nonetheless, can be dual. In some years, large amounts of allochthonous organic matter can lead to suppression of both species by clogging their filtration system. In other periods, runoff can lower water transparency thereby reducing the hunting efficiency of plankton-feeding fishes and leading to an increase in D. brachyurum abundance.