Studying the development of such an important group as cyanobacteria is an integral part of environmental monitoring of the Volga-Caspian region. Based on long-term data, a comparative description of the current state of the group of cyanobacteria of the Volga-Caspian region is indicated. The degree of similarity of marine and river species of the group of cyanobacteria for sections of the Volga River, Northern and Middle Caspian Sea was determined.
