Lipid peroxidation in tissues of pike Esox lucius Linnaeus, 1758 and roach Rutilus ruti‑ lus (Linnaeus, 1758) from Lake Kostomukshskoe (storing tailings from the Kostomuksha ore mining and processing enterprise) was found to be more intensive than in fish living downstream the Kenti River. The content of lipid peroxidation products in the liver of fish from Lake Koivas was significantly lower than in fish living higher up the Kenti River. This may be due to significant differences in the concentration of ions in these water bodies. A high level of primary lipid peroxidation products – diene conjugates and diene ketones, was detected in the liver of roach and pike from the tailing pond, indicating the activation of the initial stages of peroxidation in fish tissues in response to a high level of minerals from the tailings pond. Among all the studied fish tissues the highest level of lipid peroxidation products was found in gills. This can be explained by the higher degree of oxygenation in this organ and, as a consequence, enhanced oxidation of membrane lipids in gills. The high mineralization of the Kostomuksha mining plant’s tailing dump creates an unusual, hypertonic habitat for freshwater fish. This affects, above all, the functioning of their gills, which regulate the body’s water-salt balance. Fine suspended solids in Lake Kostomukshskoe reduce the oxygenation of gills in roach and pike, thus affecting the rate of peroxidation processes. The tissue with the lowest content of lipid peroxidation products was muscles. The activity of peroxidation processes in muscles showed no significant variation among fish from different waterbodies. Fish from Lake Koivas (the farthest away from the industrial source) demonstrated the lowest degree of tissue peroxidation. The activity of peroxidation processes declines in the following sequence: gills-liver-muscles. The most pronounced variation in the content of lipid peroxidation products was found in the liver, presumably due to the high metabolic and detoxification activity of this organ. Based on the analysis of the studied parameters in the two fish species, pike is more resistant to industrial impact, most likely due to the characteristics of its ecology