A long-term assessment of the toxicological condition of certain areas of the Uglich reservoir is given based on the results of bioassay of water and bottom sediments. During the research period 2012–2020, there was a tendency of the toxicity reduction of water in all sections of the reservoir. The maximum values of reproductive indicators of Ceriodaphnia affinis were registered in 2019. The toxicity of bottom sediments had a slight tendency to decrease in the upper section of the reservoir and did not change in the middle and lower sections. During the teratological study of the Uglich reservoir in 2012–2013 years it was found that the proportion of chironomid larvae with pathomorphological changes in the structures of the mouth parts during the observation period was on average 14.5%, which is higher than the established control (6.7–7.0%) and background values (0–8.0%). The results of the bioassay are confirmed by analytical data on water and sediment pollution. Significant differences in the pollution coefficient of water between the reservoir areas, both in individual elements and in total, have not been recorded. The highest values of the total and average pollution coefficient were reached in the middle section, where higher concentrations of Cu and Zn were determined. Despite the tendency of decreasing concentrations of Cr, Ni, Cu, Zn, Cd and Pb in the bottom sediments of the reservoir, the levels of Cd, Cr, Ni and Zn exceeded their background concentrations established for the Upper Volga basin.

A comprehensive assessment of the ecotoxicological state of the reservoirs of the Middle and Lower Volga was carried out using the method of biodiagnostics (biomarking, biotesting) and analysis of the content of heavy metals in bottom sediments. The spatial variability of the content of heavy metals in bottom sediments and the values of biomarkers of the state of oxidative stress in the liver of bream from different reservoirs was established. The toxicity of bottom sediments was determined. According to the results of the study, it is possible to arrange the reservoirs according to the degree of deterioration of the ecotoxicological state in the following order: Gorky > Volgograd = Saratov > Kuibyshev > Cheboksary. The Rybinsk reservoir in the area of station 1 can be taken as a background area in terms of anthropogenic load.