Impacts of sediments and heavy metals on the biota of streams in the copper-mining district of southwestern Montana were examined by comparing aquatic communities of impacted streams with those of control streams. These results revealed that: chemical and physical habitats at the impacted sites were disrupted, the presence of trout was an inadequate measure of ecological integrity for these sites, and watershed classification based on a combination of mapped terrestrial characteristics provided a reasonable method to select control sites where potential control sites upstream and downstream were unsuitable. Refs.