Effects of the High-Pressure Bratsk Hydroelectric Power Station on the Zooplankton of the Bratsk Reservoir.

When studying the ecological effects of the influence of a hydroelectric power station (HPS) dam on the zooplankton of the regulated section of the Angara River and the effect of the zooplankton downstream drift on the feeding conditions of fish of the Bratsk Reservoir during the vegetation period of 2022, it has been established that water column stratification is a significant factor in the ecological differentiation of plankton communities from the upper reaches of the Bratsk HPS. Relative to the heated epilimnion layer, a specific, poor in species, low-abundant and low-productive plankton, entering the dam water intakes, deve-lops in the cold-water hypolimnion. A rigorous analysis revealed no transformation in the composition of communities, a statistically significant decrease in abundance and productivity, and an increased mortality of invertebrates during the transition through the dam, as well as a deterioration in the ecological quality of water in the lower reaches of the HPS. Zooplankton (both alive and dead) drifting downstream from the re-servoir constitute a significant portion of the diet of fish, which get as close as possible to the HPS during feeding and form clusters that are denser than those in the water area of the Bratsk Reservoir. The data indicate the efficient adaptation of the lake–river planktocenosis to a specific natural and technogenic mode of operation of a large hydraulic structure. Locally, the Bratsk HPS has no ecologically significant negative effect on the plankton of the Bratsk Reservoir and Angara River and it has a positive effect on the fish population of the lower reaches through the enrichment of its forage base. [ABSTRACT FROM AUTHOR]