We designed an in situ assay for investigating macroinvertebrate drift behavior in response to a point source of environmental pollution. As a model, we used Cinygmula nymphs to assess both the presence and level of copper contamination in a stream that was polluted with effluent from an abandoned copper mine. The study showed that Cinygmula exhibited increased tendency to drift with increased exposure to aqueous copper. Cinygmula drift behavior exhibited graded responses to increasing concentrations of aqueous copper up to and including 78 ppb. The results indicated that a simple yet sensitive in situ bioassay could be used to detect environmentally important levels of copper contamination in Haggarty Creek.