Results of 2-years' quantitative sampling of benthic macro-invertebrates in Mink Creek are reported. Midway through the study the substratum and flow pattern were intentionally altered. The invertebrate community consisted of 90 taxa, of which Trichoptera and Plecoptera were the best represented. However, Ephemeroptera were the most important in terms of numbers and biomass. Mean density of the community increased from 7000/m2(10.8g AFDW) in year 1 to 21,000/m2(26.5g) in year 2. In spite of the apparent increase in carrying capacity of the stream in year 2, community structure as measured by species richness, diversity, equitability and relative importance at the ordinal level did not differ between years. Grazers made up 42 and 33% of total numbers and 56 and 52% of total biomass in the two years respectively. Collectors constituted 50 and 78% of numbers and 20 and 22% of biomass. Most populations showed consistent seasonal patterns in the two years. These appear to be due to “keyed” responses of the fauna (hatching, emergence) to predictable patterns of discharge and temperature as well as to catastrophic effects of floods. Although monthly values for richness, diversity, and equitability were similar in the two years, they varied more during year 1.