The activity of lysosomal enzymes (β-glucosidase, β-galactosidase, DNAse, RNAse, acid phosphatase) in the organs of roach Rutilus rutilus L., inhabiting a pure lake (Lake Kamennoe) and two reservoirs of the lake-river system Kenti – Kento, receiving ore mining and processing wastewater (from "Karelskiy Okatysh" mill), was investigated. Significant changes in the enzymatic activity between fish from the upstream lake (Kostomukshskoe, converted into a tailings dump) and the downstream lake (Koivas, with the wastewater far more diluted) were revealed. It was shown that the activity of acid phosphatase and nucleases in the liver and gills of roach inhabiting the tailings dump was higher than the activity of these enzymes in fish from Lake Koivas, which can be an indirect indicator of biosynthetic processes intensification and mobilization of defense mechanisms in organisms. The adaptive increase in β-glucosidase activity was marked. It indicates the involvement of glucose-containing components in the anaerobic processes of energy supply to an organism under the influence of mineral pollution. The dependence of biochemical responses in fish on the composition and intensity of water pollution by ore mining and processing wastewater is discussed.