Analyses of the suspended particulates in lakes within a 30-km radius of the smelting complex at Sudbury show average Ni, Cu, Zn, and Pb concentrations of 1500, 420, 540, and 360 mug g-1, respectively. Organic matter constitutes 35-60per thousand of the suspended material in the lakes but plays a minor role in the transport of metals to the sediments. The rates of metal accumulation in the sediments have been estimated typically to be 100-600, 50-300, 10-60, and 5-30 mg m-2 year-1 for Ni, Cu, Zn, and Pb, respectively. The enrichment factors for metals in surficial sediments typically are 12-115, for Ni, 10-77 for Cu, 2-10 for Pb, and 2-8 for Zn. These enrichment factors and deposition rates for Ni and Cu are among the highest recorded anywhere in the world. Some of the lakes with pH values of 4.5 or less show no enrichment or accumulation of polluntant metals in their surface sediments, indicating that pollutant metals previously stored in the sediments have leached away. This documentation that the contaminated sediments can release substantial quantities of toxic metals to the overlying water must have interesting ramifications with regard to the limnological impacts of acid rains.