This dataset is comprised of water quality data and benthic macroinvertebrate data collected from basins in Colorado, USA, and Finland. The data includes ancillary water quality characteristics but also a suite of trace metals observed at each site. Also included are modeled outputs that characterize the bioavailability of each trace metal to a biotic ligand. These data were used to explore the importance of metal toxicity and pH as stressors on benthic macroinvertebrates characterized as the number of unique Ephemeroptera + Plecoptera + Trichoptera genera observed at each site. An interpretive summary of the work follows. One of the primary goals of biological assessment of rivers is to identify whether contaminants or other stressors limit the ecological potential of running waters. Quantitative relationships between species richness and environmental gradients are useful to better understand biodiversity patterns. Many studies have focused on the effects of pH and high metals concentration on freshwater macroinvertebrate community but, due to data limitation and the lack of tools, the ecological effects of metals mixture in streams are less studied and still unclear. We address an old question: is it the low pH or the metals that are deleterious for stream ecosystems? With new tools, we can achieve improved understanding of the true importance of the two stressors. Our study quantified the limiting effects of pH and chronic metal toxicity for macroinvertebrate community richness. We verified that current environmental quality standards for metals are protective of aquatic biodiversity and proved that pH has a direct limiting effect on richness and it not acts only via modifying the availability and the toxicity of metals. These questions were applied to a dataset spanning two continents and diversity of geologies and ecosystems providing a broad basis for understanding how physico-chemical conditions limit global freshwater biodiversity.