Riffle beetles (Elmidae:Coleoptera) are commonly used as biological indicators of unpolluted, well-aerated stream conditions. However, macroinvertebrate samples from streams in southeastern Ohio (N > 40) revealed high densities of riffle beetles at sites impacted by high acid, sulfur and metal loadings. In laboratory assays, adult Stenelmis, Macronychus and Dubiraphia tolerated acute acid exposure (pH=3.0 for 72 h) with little or no mortality (< 5%). Riffle beetles appear to be much more tolerant of acid mine pollutants than other anthropogenic stressors from agricultural or industrial/urban activities.