The study conducts a comprehensive analysis of the water quality and toxicology indicators of the Verkhnetobolskoye and Karatomarskoye reservoirs in northern Kazakhstan to identify potential pollutants, including heavy metals, organic and inorganic substances, and pesticides, and to assess the influence of these parameters on the suitability of water for various uses. The study combined hydrochemical and toxicological analysis, including atomic absorption spectrometry, gas chromatography–mass spectrometry, and ion chromatography to detect heavy metals, pesticides, and organic pollutants. The data were analyzed using statistical methods to determine correlations between different pollutants and to assess overall water quality according to national and international standards. The analysis suggests that both reservoirs are subject to moderate or severe pollution. Elevated concentrations of heavy metals, especially cadmium and zinc, were detected at several sampling points, exceeding the threshold limit value for safe water use. Although the levels of most pesticides are within the required limits, trace amounts of chlorinated pesticides were detected. The water quality in both reservoirs is classified as bad (class 4), with a high content of suspended solids, magnesium, and sulfates, making this water unsuitable for domestic use without thorough treatment. The reservoirs remain suitable for industrial uses, including irrigation and mining. The findings underscore the need for stricter water quality monitoring and improved water purification infrastructure in the reservoirs of Kazakhstan.