Abstract. The environmental impacts of acid mine drainage (AMD) at different levels of dilution were evaluated using transplanted Asian clams (Corbicula j/uminea) and qualitative benthic macroinvertebrate community sampling. Three contiguous streams in the upper Powell River watershed were sampled/tested at sites upstream and downstream of AMD inputs. The first stream was considered small according to its relative flow (-0.1 relative units at downstream site), the second was medium sized (-0.4 relative units), and the third was large (-1.0 relative units). For the small stream, total invertebrate richness, Ephemeroptera-Plecoptera-Trichoptera (EPT) richness, and percent mayfly abundance were significantly lower downstream of AMD inputs compared to upstream sites. In the medium sized stream, only percent mayfly abundance was impaired downstream of AMD, while in the large stream, total richness and EPT richness decreased nominally downstream of AMD inputs. Multiple linear regression analysis suggested that water colnmn conductivity was a good predictor of both total richness (R 2 = 0.819, p = 0.0050) and EPT richness (R 2 = 0.836, p = 0.0039), with increasing conductivity being associated with lower richness values. Clam survival decreased at the downstream site in the small stream, while clam growth was impaired at downstream sites in the medium and large streams. Water column pH was the best predictor of clam survival (R 2 = 0.886, p = 0.0016) while aluminum, conductivity, iron and flow described clam growth (R 2 = 0.999, p = 0.0015). These fmdings suggest that AMD inputs may be impacting streams beyond the zone of pH depression, even where flow was equal to approximately ten times the flow of the small, most severely impacted stream.