Using a biplate substrate sampler, aquatic macro-invertebrates were collected during the fall, winter and spring seasons at the confluence of the Mississippi and Chippewa Rivers along the Minnesota-Wisconsin border. The substrate sampler proved very desirable in pointing out extreme community variations which existed between the two rivers. It was found that the members of a downstream community were a blend of the communities present in upstream tributaries. However, as compared with upstream communities, a shift in dominant organisms occurred. Striking seasonal changes appeared in the invertebrate populations as well as the environment of the rivers. All sampling revealed clean water communities were present and suggested the absence of aquatic pollution
