 The zooplankton communities of two thermocarst lakes on Samilov Island, Lena River Delta, Yakutia, are composed of rotifers, large copepods, and cold water-dwelling northern species. These species determine the community structure and biomass values. The lake's seasonal dynamics are characterized by high-suprobity indices and low-species diversities. This article was authored by L.A. Furlova and G.R. Nikomatsyanova.