Hartley Creek, a tributary of the Muskeg River in the Athabasca Oil Sands area of northeastern Alberta, has a discharge ranging between 0.5 and 7 m3.s-1 , experiences temperatures ranging between 0° and about 18°C, and has high oxygen concentrations at all seasons. The benthic fauna is rich and diverse and is dominated numerically by Chironomidae but by Trichoptera in terms of biomass. Each of the four principal substrate types found in the pools has a distinctly different benthic community. The riffle benthic communities are different from the benthic communities of the pools. The \"single-rock\" sampling technique has shown that the microdistribution of trichopteran larvae is influenced by both rock size and the presence or absence of moss cover. Host of the aquatic insects are univoltine (producing only one brood per year) with spring or summer emergence. A few species (some Chironomidae, Baetinae) may be multivoltine and at least one species takes at least three years. Invertebrate drift displays a typical diel cycle with morning and evening peaks. Predominant benthic components include Baetinae and Chironomidae but Cladocera and Copepoda are also abundant and are derived from pools. Temperature and discharge both exert profound effects on structure and composition of the benthic communities but none of the chemical factors measured appears to be a significant influence. The benthic communities of the riffles are different from those of the pools.