The valley of the South Fork Coeur d’Alene River and some of its tributaries have been heavily impacted by the dispersion of metal-enriched materials from the Coeur d’Alene mining district since 1884. The valley floor, including the unconsolidated valley-fill/flood-plain aquifers, is a major holding area for mine tailings. The U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, characterized groundwater and surface-water relations for parts of the South Fork Coeur d’Alene River Basin and quantified the loading of dissolved metals into the South Fork Coeur d’Alene River system from groundwater seepage. This information can be used to determine the effects of dissolved metal from ground-water seepage on the river system and to evaluate the necessity and feasibility of remediation along gaining reaches. This study defines a field approach that can be repeated during and after the implementation of remediation solutions to measure the effectiveness of these efforts in reducing loading to streams. The study area includes three reaches along the South Fork Coeur d’Alene River valley in the Coeur d’Alene mining district in central Shoshone County, northern Idaho: a 3.3-mile reach of Canyon Creek at Woodland Park, a 4.8-mile reach of the South Fork Coeur d’Alene River near Osburn, and a 6.5-mile reach of the South Fork Coeur d’Alene River near Kellogg and Smelterville. Seepage studies were conducted during July 27–29; September 17–19; and October 15–17, 1999. Each seepage study was conducted over a 3-day period, during which each station was measured on a daily basis for streamflow, and waterquality samples were collected. The consecutiveday approach allowed for an evaluation of variability in streamflow gains and losses and metal loading that resulted from changing hydrologic conditions. During the July, September, and October seepage studies, ground-water seepage was the predominant source for gains in dissolved cadmium and zinc loads in the three study reaches, whereas tributary inflow loads were a minor source. The overall average net gain in dissolved zinc load from ground-water seepage into the South Fork Coeur d’Alene River near Kellogg and Smelterville was about 730 pounds per day, compared with the net gains in Canyon Creek at Woodland Park and the South Fork Coeur d’Alene River near Osburn, which were roughly similar at 150 and 218 pounds per day, respectively. The net gain in dissolved cadmium load from ground-water seepage into the three river reaches was about two orders of magnitude less than the gain in dissolved zinc. On the South Fork Coeur d’Alene River study reaches near Osburn and near Kellogg and Smelterville, no pattern associated with an increase or decrease in dissolved lead load along gaining or losing subreaches was recognizable. Canyon Creek at Woodland Park was the only study reach where ground-water seepage contributed appreciably to the dissolved lead load; the average net gain was 1.5 pounds per day. The average dissolved lead loads leaving South Fork Coeur d’Alene River study reaches (corrected for tributary inflow along the study reaches) near Osburn and near Kellogg and Smelterville were 1.4 and 0.8 pounds per day less, respectively, than the loads entering the study reaches. The decrease in dissolved lead could be the result of lead adsorbing onto organic and inorganic sediment surfaces and (or) coprecipitating with iron and manganese oxides. These forms of lead likely will be resuspended into the water column at high flows.