Water scarcity, security, and deterioration of water quality have been serious environmental issues in Central Asia. This study has investigated the contamination of the Esil river, the only transboundary river originating in Kazakhstan, and implemented the human health risk assessment of heavy metals (HMs; Cd, Pb, Cr(VI), and As) in its relevant 15 surface water bodies. HM concentrations in 2893 water samples were measured over 6 years (2014–2019). The river’s water quality was classified between “marginal” and “good,” but nine sites revealed worsened quality during the period. The monitored HMs’ median concentrations followed a decreasing order of Cr(VI) (0.0015 mg/L) = As (0.0015 mg/L) > Pb (0.0009 mg/L) > Cd (0.00005 mg/L). Human-induced behaviors, especially industrial activities, were observed to influence the water quality negatively. Due to the growth of cities, municipal wastes and the release of pollutants during construction activities were potential origins of HMs, too. Two exposure scenarios for the human health risk assessment were investigated: the risks from a recreational activity scenario were acceptable, but concerning values were obtained from a household use scenario, including seven sites with hazard index (HI) > 1 and a maximum cancer risk of 7.22 × 10–4.

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