<p>The presence of elevated heavy metals in water is a key factor in evaluating potential risks to human health. The concentration of Cd, Pb, Ni, Cr, and Zn in surface water and sediment in an impounded karst lake, Lake Caohai, China were quantified. The abundance of water-bound Cd, Pb, Ni, Cr, and Zn were within the acceptable range, while the concentrations of Pb, Cr, Ni, and Zn in lake water exhibited a positive correlation with their respective concentration in lake sediments (R² = 0.36–0.54, <i>P</i> &lt; 0.01). The partition coefficients revealed that Cd, Cr, Ni, Pb, and Zn were more likely to enrich in the sediments. The heavy metal pollution index and toxicity load of water samples were found to be below the critical threshold. 95th percentile values of the hazard quotient for water-bound Cd, Pb, Ni, Cr, and Zn were all below the acceptable limit value of 1, the hazard quotient of Cd, Pb, Ni, Cr, and Zn in children was higher than in adults. Exposure duration was the most efficient contributor in determining the probability of hazard quotient for Cd, Pb, Ni, Cr, and Zn. Future research should focus on the complex interplay of exposure variations and hydro-geo-chemical processes to improve the accuracy of risk characterization.</p>