Abstract <p>The paper presents the first results of a comprehensive study of plankton communities in Lake Murakanskoye located in the National Park “Onezhskoye Pomorie”. The qualitative and quantitative indicators of phyto- and zooplankton are shown, and the structure of the communities is considered. It was revealed that plankton communities in the summer of 2023 were characterized by a poor species composition and low overall quantitative development: the average biomass of phytoplankton and zooplankton was 0.34 ± 0.09 g/m³ and 509.1 ± 112.4 mg/m³, respectively. The main background of zooplankton in terms of quantitative composition is copepods; in the phytoplankton composition, diatoms and green microalgae are prevalent. Based on the indicators of plankton development, the lake is characterized as oligotrophic. Saprobiological analysis of the indicator species of zooplankton showed that the lake waters had an oligosaprobic level and corresponded to quality class I. In general, the ecological state of the surveyed reservoir can be assessed as good.</p>