This paper presents the results of long-term monitoring (2019–2026) of Zn, Ni, Fe, Cu, Cr concentrations in surface waters and bottom sediments of the Kuibyshev Reservoir near Ulyansk city. The average concentrations of Zn, Ni, Fe, Cr exceed the maximum permissible concentrations for fishery water bodies by factors of 1.6–4.4. Hierarchical clustering and K means methods identified three groups of metals: seasonally dependent (Fe, Ni, Zn), conservative (Cu), and metals with signs of a point anthropogenic source (Cr). The interphase distribution coefficients lgKd were calculated: 3.35–3.39 for Cu and Zn, 2.80 for Ni, and 2.22 for Fe, indicating different accumulation capacities in bottom sediments. Using multiple linear regression, empirical relationships between metal concentrations and water temperature and pH were obtained. A forecast for the spring period of 2027 predicts exceedances of MPC: Fe – 7.9 times, Zn – 2.3, Ni – 1.6, Cr – 1.7 times. Copper remains the only metal with concentrations below the standard. The obtained results can be used to improve environmental monitoring systems and predict water quality in large lowland reservoirs.