List of longest rivers of Canada
Nine rivers in this list cross international boundaries or form them. Four—the Yukon, Columbia, Porcupine, and Kootenay—begin in Canada and flow into the United States. Five—the Milk, Pend d'Oreille, Saint Lawrence, Red, and Saint John—begin in the United States and flow into Canada. Of these, the Milk and the Kootenay cross the international border twice, the Milk leaving and then re-entering the United States, the Kootenay leaving and then re-entering Canada. The drainage basins of these nine rivers extend into both countries; in addition, the drainage basins of six others—the Fraser, Assiniboine, South Saskatchewan, Saskatchewan, Nelson, and Winnipeg—extend into the United States even though their main stems flow entirely within Canada.
Nutrient cycling in the Columbia River Basin
Beginning in the 1930s with the construction of the Bonneville and Grand Coulee dams, the Columbia River has experienced significant modification to its flow. Today, the US Army Corps of Engineers recognize over 250 reservoirs, 150 hydroelectric projects, and 18 mainstem dams on the Columbia and its main tributary, the Snake River. Dams have been shown to directly impact nutrient cycling within the Columbia river basin through the formation of reservoirs which dramatically alter river hydrology and discharge rates and as a result constitute a major anthroprogenic impact on nutrient cycling in the river. Due to its size and the large number of dams within the basin, the Columbia River basin is often used as representative case study on how dams an impact nutrient cycling of watersheds in general. Notably, dam construction in the Columbia River Basin has impacted relative nutrient ratios, methane production, and salmon migration.