1. Introduction: Metal contamination is a widespread environmental problem in waterways worldwide, and managing its ecological influence on affected streams and rivers remains a major challenge (Luoma and Rainbow, 2008). The main sources of metals entering waterways are mines. Mines are ongoing sources of metal contamination, and even abandoned ones can still leak metals into streams and rivers (Abel, 1996; Brown, 1977; Byrne et al., 2010; Maret et al., 2011; Thornton, 1983; Distinguishing the effects of high metal bioavailability on benthic macroinvertebrates in mining-affected streams is not easy without resorting to complex multivariate statistics to relate any observed changes in community composition to changes in an environmental parameter such as a concentration of metals measured in certain environments. component. Dose-response curves that define metal toxicity in laboratory experiments (e.g., in single species and in single chemical bioassays) are limited in their ability to be applied to relatively complex natural water systems (Luoma et al., 2010). The larvae of caddisfly species of the genus Hydropsyche (order Trichoptera) is a common inhabitant of temperate freshwater streams, including metal-contaminated systems (Cain et al., 2004; Luoma et al., 2010; Rainbow et al., 2012). They have been shown to be reliable freshwater biomonitors of high bioavailability of toxic metals such as copper, and can be used as a tool to assess metal exposure in these contaminated freshwater habitats (Cain et al., 2004 ; Luoma et al., 2010; Rainbow et al., 2012). Macroinvertebrate communities are affected by the elimination or reduction in numbers of certain taxa in metal-contaminated areas...... middle of article ......The first evidence supporting this hypothesis was provided by Luoma et al. (2010) in the Clark Fork River in the United States, reinforced by subsequent data from a number of rivers in southwest England (Rainbow et al., 2012). This study explores two Cornish catchments examined by Rainbow et al. (2012) in more detail, with both catchments having a history of metal mining (Gower et al., 1994). This more detailed study of Cornish waterways is part of a wider study to determine whether a methodology applicable to freshwater habitats contaminated by mining in the United States and England is transferable to a wider study of ecotoxicology in watercourses affected by mining effluents in Poland. The present study was carried out by measuring concentrations of bioaccumulated metals in Hydropsyche siltalai and assessing the abundance of mayflies in the River Red and River Hayle in Cornwall, southwest England..