This report reviews and summarizes available information on aquatic biological communities in the Willamette Basin through 1995. Specifically, the report describes (1) the distribution, abndance, and trends of three taxonomic groups--algae, macroinvertebrates, and fish--and, to a lesser degree, other selected semi-aquatic taxa (i.e., taxa frequenting but not living wholly in water), including amphibians and reptiles, birds, and mammals, (2) the types of aquatic and riparian habitat that support and influence aquatic communities and their biotic constituents, (3) the natural and human-associated impacts on that habitat and associated biological communities, amd (4) the levels of enviroinmental contaminants to which biological communities and specific biota are exposed. The information in this report is intended to aid in the identification of data gaps relative to taxa and geographic areas, and to stimulate collaboration and increase coordination in present and future ecological research in the Willamette Basin.