One of the objectives of this project was to identify spatial patterns of nutrient limitation in the Athabasca and Wapiti-Smoky rivers. Two experiments were conducted to accomplish this goal. The first experiment used nutrient diffusing substrata (NDS) downstream of the Hinton combined effluent to identify the interactive effects of both nutrient enrichment and herbivory (grazing by aquatic insects) on algal biomass. The second experiment used NDS to quantify large scale patterns in algal biomass and nutrient limitation, with four levels of nutrient enrichment, upstream and downstream of the major effluent and tributary input sources along the Athabasca and Wapiti-Smoky rivers.