The aim. Study of the ecological state of the Voronezh reservoir under conditions of “blooming” of water by cyanobacteria. Materials and Methods. EEvaluating water quality data of hydrochemical analysis, assessment of suspended solids distribution and temperature in the water area, materials of hydrobiological study (phytoplankton), microcystin content in water have been taken into account. Results and Discussion. The direction of anthropogenic changes occurring in the ecological state of the reservoir has been traced for 2016–2022.