Abstract
Mercury in fifteen rivers and two lakes was measured to determine a background level of mercury in fresh waters. Mercury in unpolluted fresh waters contained concentrations between 1.0-5.1 ng/l, which approximate sea water values. Since mercury concentration in precipitation is ca. 1 ng/l, mercury levels in the world's rivers would be expected to be similar to those in Japanese rivers. Mercury was one order of magnitude higher in rivers receiving wastes from mercury mines than in unpolluted waters.
