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The pollution of surface waters has be-come rampant, which has led to the degrada-tion of many fishery reservoirs. The variety of toxicants entering water bodies in various ways is extremely large and is constantly being replenished with new substances. Their impact on aquatic organisms is associ-ated with the development of pathological processes, degradation of populations up to their death. This is especially evident in the main object of the use and protection of fish-ery reservoirs - fish. First of all, the most valuable species of whitefishes and salmon-ids suffered in the North-West region. The paper considers one of the main problems of fisheries in the North-Western region of Russia – the decrease in fish stocks and catches in natural reservoirs, and reveals the main reason for this ongoing process - the violation of natural and factory reproduction of fish and invertebrates due to the influence of a toxicological factor. This primarily affected the most valuable fish species - salmonids, white-fishes, pike perch. It has been shown that in recent years in Lake Ladoga (especially in its southern shallow zone, the main breeding and feeding zone of many fish species) and other reservoirs of the region, the negative situation of violation of repro-duction of fish and invertebrates (fish food supply) has significantly worsened, which has had a very negative impact, including the decline in the catch of especially valuable fish resources. Measures to prevent negative events are in-dicated. The need to take urgent measures to reduce the flow of pollutants into Europe's largest Lake Ladoga and other important fisheries reservoirs in the North-West region is emphasized.

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The article presents the materials of biological and chemical-analytical studies of the Shlisselburg Bay of Ladoga lake, that plays an important fishery and sanitary-hygienic role as a source of water supply of St. Petersburg. The dominant role of ichthyo-fauna in the assay of the ecological and toxicological state of the studied water area is shown. The purpose of the conducted research is to assess the ecological and ichthyo - toxicological state of the Shlisselburg Bay of Ladoga lake, as one of the main fishery water areal and the only source of water supply of St. Petersburg (the source of the Neva River). Biological and chemical analytical studies of the water area of the Shlisselburg Bay in laboratory conditions were carried out in the summer-autumn period in 2022 in three water areas. A feature of the Shlisselburg Bay is the presence of a runoff flow, that initiates the removal of pollutants and the nature of bottom sediments, which makes the Bay less vulnerable to anthropogenic impact. Currently, the methods used to assess water quality for the fisheries perspective are biological – bioindication and biotesting, as well as the results of chemical analysis in comparison with the standards for the content of harmful substances in water, sediments, precipitation and fish. Preference is given to “express’ methods: biotesting and bioindication of fish research results. Analysis of materials from previous studies have given reason to consider a gradual decrease in anthropogenic load (exposure to pollutants) on fish, as generally recognized indicators of water quality, given from fisheries positions. The results of the research showed that the ecological and toxicological condition of the Shlisselburg Bay has now improved, but cannot be considered satisfactory. Taking into acount the state of the ichthyo fauna and the level of its pollution, it can be characterized as weakly expressed sublethal with a possible transition to medium-expressed, conditionally sublethal in the spring period.