show Abstracthide AbstractUsinsky Bay is a freshwater estuary about 50 km long, formed as a result of flooding of the lower section of the Usa River valley after the construction of the Kuibyshev hydroelectric power station and the formation of the Kuibyshev reservoir.The project aims to study the changes in the diversity and composition of prokaryotic and microbial eukaryotic plankton communities along the long axis of the bay.