Water, bed sediment, and biota were sampled in streams from Butte to below Missoula as part of a program, conducted in cooperation with the U.S. Environmental Protection Agency, to characterize aquatic resources in the upper Clark Fork basin of western Montana. Sampling sites were located on the Clark Fork, five major tributaries, and three smaller tributaries. Water-quality samples were collected periodically at 17 sites during October 2003 through September 2004 (water year 2004). Bed-sediment and biological samples were collected one time in August 2004. The primary constituents analyzed were trace elements associated with tailings from historical mining and smelting activities. This report summarizes the results of water-quality, bed-sediment, and biota samples collected in water year 2004 and provides statistical summaries of data collected since 1985. Water-quality data for samples collected periodically from streams include concentrations of selected major ions, trace elements, and suspended sediment. Daily values of suspended-sediment concentration and suspended-sediment discharge were determined for three sites. Bed-sediment data include trace-element concentrations in the fine-grained and bulk fractions. Biological data include trace-element concentrations in whole-body tissue of aquatic benthic insects. Quality-assurance data are reported for analytical results of water, bed sediment, and biota. Statistical summaries of water-quality, bed-sediment, and biological data are provided for the period of record since 1985 for each site.