This project, which was a continuation of 1976-77 activities of AOSERP Project AF 2.0, "Interim Report on Ecological Studies on the Benthic Invertebrates of Various Rivers in the Alberta Oil Sands Environmental Research Program Study Area, Northeastern Alberta", was to describe the basic ecology of aquatic benthic macrofauna of the Athabasca River and its major tributaries, the Muskeg and Steepbank rivers. The effect of habitat (including oil sands formations) on the diversity of the invertebrate populations and algal and bacterial responses to substrates treated with synthetic oil also were studied. Such basic taxonomic and life cycle data are required to support future manipulative and experimental studies designed to describe and predict changes in benthic communities that can be expected from oil sands development activities.