Abandoned mine lands contribute to significant water-quality degradation in the Beaver Creek watershed in northern Idaho. Streams in this watershed drain the northern flank of the Coeur d’Alene mining district, one of the world’s largest producers of silver and one of the country’s major historical producers of lead and zinc for more than 100 years. Effective cleanup of these streams will depend on accurate characterization of metal concentrations in streams and various sources of these metals. Cadmium, lead, and zinc loads entering Beaver Creek and its major tributary, Carbon Creek, were quantified, and source areas for these metals were assessed during May and June 2002. Metal loads were calculated for main-stem and surface-inflow sites by combining measured streamflow with dissolved cadmium, lead, and zinc concentrations analyzed in waterquality samples collected during three synoptic sampling events. To assess the effects of surface and shallow subsurface inflows on the gain or loss of streamflow and metal loads, Beaver and Carbon Creeks were divided into subreaches. Four subreaches were defined on Beaver Creek using five main-stem sampling sites (UBC3, UBC5, UBC8, BC10, and BC14); two subreaches were defined on Carbon Creek using three main-stem sampling sites (CC2, CC6, and CC9). During each of the synoptic sampling events, concentrations of cadmium and zinc were highest in samples collected at the Carlisle Mine adit between sites CC2 and CC6. During two of the three synoptic sampling events, the concentration of lead was highest in samples collected from a left-bank seep downgradient from the Idora Mill between sites UBC3 and UBC5. The largest identified cadmium and zinc source to Beaver Creek is the surface inflow from Carbon Creek (between sites UBC8 and BC10), which accounted for 45 to 72 percent of the main-stem cadmium load and 49 to 89 percent of the main-stem zinc load in Beaver Creek. Another large source of cadmium and zinc to Beaver Creek is subsurface flow through the tiered flotation tailings pile near Carbon Center (between sites BC10 and BC14) into Beaver Creek. Amounts of lead contributed by source areas to Beaver Creek vary with streamflow conditions. During high streamflow, the largest source of lead to Beaver Creek is the remobilization of fine-grained (less than 0.45-micrometer), lead-enriched particulates from the streambed throughout the study area. During low streamflow, bank seepage of subsurface water into Beaver Creek in the subreach downgradient from the Idora Mill (between sites UBC3 and UBC5) is the major source of lead to Beaver Creek. During each synoptic sampling event, Carbon Creek is a major source of lead to Beaver Creek. The Carlisle Mine adit (between CC2 and CC6) is the largest source of cadmium and zinc to Carbon Creek and, ultimately, to Beaver Creek, and accounted for 57 to 88 percent of the total main-stem cadmium load and 56 to 88 percent of the total main-stem zinc load in Carbon Creek during each of the synoptic sampling events. Another source of cadmium and zinc to Carbon Creek is resurfacing cadmium- and zincenriched hyporheic flow (possibly originating from the Carlisle adit or the Carlisle Mill) between sites CC6 and CC9. As in Beaver Creek, amounts of lead contributed to Carbon Creek by source areas vary with streamflow conditions. During high streamflows, increased discharge from the Carlisle Mine adit appears to be the largest source of lead to Carbon Creek; during low streamflows, resurfacing lead-enriched hyporheic flow appears to be the major source of lead to Carbon Creek.