COMPREHENSIVE CHARACTERIZATION OF THE STATE OF THE BUKHTARMA RESERVOIR BASED ON MULTI-YEAR OBSERVATIONS (2014...2025)

The Bukhtarma Reservoir, the largest water body in the upper course of the Irtysh River, plays a key role in the water-management complex of East Kazakhstan, combining hydropower generation, flow regulation, water supply, and fisheries. The intensive development of the region’s mining and metallurgical industries is accompanied by inputs of heavy metals into the ecosystem-substances notable for persistence, mobility, and a propensity for bioaccumulation. This study synthesizes state monitoring data from RSE «Kazhydromet» for 2014...2025 together with national and international research on water, bottom sediments, and aquatic organisms. Еhe reservoir’s hydrochemical parameters are generally stable: the water exhibits a slightly alkaline pH, an adequate dissolved-oxygen regime, and moderate mineralization (TDS). Copper and manganese are the main elements shaping the toxicological profile; in certain years their concentrations reached 3.9 µg/dm³ and 24.0 µg/dm³, respectively-linked both to localized technogenic impacts and to natural processes of secondary remobilization from bottom sediments. Zinc, nickel, lead, and cadmium mostly remained at background levels. Localized hotspots of elevated metal accumulation and bioaccumulation in fish tissues were identified.