This dataset is from the fourth of four experiments which test the toxicity of several metals with aquatic insect communities that were colonized in the field and then transferred and tested in experimental streams. Here we report original data from testing the toxicity of cobalt (Co), copper (Cu), and nickel (Ni), singly and in mixtures, to natural benthic communities including aquatic insect and algal communities. The methods are the same as those used in Experiment 3, except for the metals combinations. Trays of cleaned gravel were placed in a stream (the Cache La Poudre River, Colorado) and allowed to colonize for about 40 days before being translocated to Aquatic Experimental Stream Laboratory (AXL) which was located at the USGS Fort Collins Science Center. There the insects were exposed for 30 days to metal mixtures in ratios and concentrations similar to those occurring in ambient conditions. Emerging adult insects were captured and collected daily throughout the experiment, and larvae were collected at the end of the experiment. Additionally, metal residues were measured in sediments, periphyton and Brachycentrus caddisflies (a common, large-bodied, robust taxa that could survive high metals accumulations). Algal biomass responses to metals were measured in situ by in-vivo fluorescence.