The long-term goal of this study is to identify which reaches of the Athabasca, Wapiti and Smoky rivers are nutrient limited (i.e., would respond to added nutrients) and at what time of year. Laboratory and field experiments were initially performed to develop an innovative nutrient diffusing substrata that would be suitable for use in the Athabasca River. Subsequent field experiments were conducted at four sites on the Athabasca River between October and December, 1993, to identify the effects of nutrient additions on bottom-dwelling algae and invertebrate communities. The four test sites were upstream and downstream of the combined effluent discharge from Hinton and Weldwood Canada Ltd., and upstream and downstream of the discharge from the Alberta-Pacific pulp mill.