Industrial sand extraction and wastewater discharge are among the main anthropogenic factors affecting the state of the ecosystem of Lake Donuzlav (Crimea, Black Sea). Sand mining primarily significantly changes the seabed and can cause the formation of an oxygen-deficient zone. In this regard, it is necessary to continue the up-to-date hydrochemical and hydrobiological monitoring in the areas of mussel-and-oyster farms, sand mining zones, cargo port, and in the area affected by the release of the Donuzlav sewerage treatment plant. The purpose of this work is to study the hydrological and hydrochemical structure of the southwestern region of Lake Donuzlav, which is subject to anthropogenic influence and includes a zone of industrial sand mining. In April, May and September 2019, studies of the hydrological and hydrochemical structure of lake waters were carried out, including measurements of temperature, salinity, content of dissolved oxygen, five-day biochemical oxygen demand (BOD₅), alkaline permanganate oxidizability, content of silicate, mineral and organic nitrogen and phosphorus. It is shown that the spatial distribution of water temperature and salinity is characterized by great heterogeneity and temporal variability. The hydrochemical studies indicate high oxygen supply in the lake; no cases of oxygen deficiency were detected during the research period. The minimum concentrations of dissolved oxygen did not drop to the minimum allowable levels. All BOD₅ values were below the maximum allowable levels. Local anthropogenic impact on the lake waters was registered in the increased concentrations of nutrients and oxidizability values in the sand mining areas, near the sewerage outlet, in the port area and in the area affected by the domestic wastewater release.