Four effluent-impacted streams in Oklahoma, South Dakota, Montana, and Utah were evaluated in collaboration with the U.S. Environmental Protection Agency (EPA) and state agencies. Conventional aquatic test organisms and a battery of microbial activity assays were used as toxicity indicators. Microbial assays of sediment enzyme activity included alkaline phosphatase, amylase, arylsulfatase, electron transport (dehydrogenase), galactosidase, glucosidase, and protease. Study sites received refinery, municipal, and/or mining effluents and showed distinct impact and recovery zones. Significant correlations were observed between sediment enzyme activity and stream biota or chemical measurements of water quality. These positive correlations, at diverse test sites, demonstrate the utility of both short-term microbial assays and the test battery approach in environmental assessments.