Reservoirs are a special category of inland water bodies with specific features of water exchange, flow and level fluctuations. The quality of water in reservoirs is formed under the influence of three factors: natural and economic conditions for the formation of runoff in the catchment area, the quantity and quality of wastewater, atmospheric emissions of pollutants, and processes occurring in the reservoir itself. The quality of water in individual water areas of reservoirs is also heterogeneous. The article deals with the issue of the current ichthyotoxicological state of the Narva reservoir, a reservoir of fishery importance, two decades ago one of the most polluted in the North-West of Russia, which manifested itself in the total defeat of fish by toxicosis and cases of their death. This was due to a powerful anthropogenic load and the entry of pollutants in various ways, and especially by the aerogenic route. The present study is associated with a decrease in anthropogenic load as a result of a decrease in the operation of the Narva and Baltic thermal power plants (TPP). As a result of analytical studies in a number of water areas of the reservoir, it was shown that the reduction of anthropogenic load primarily affected the condition of fish as generally accepted indicators of water quality and habitat – the percentage of toxicosis damage and the severity of the pathological process decreased.

The reduction of anthropogenic load was shown by the results of biotesting and materials of chemical-analytical research.