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.
Geography of Canada
The northern parts of Alberta, Manitoba and British Columbia, most of Northwest Territories and Nunavut, and parts of Yukon are drained by the Arctic watershed. This watershed has been little used for hydroelectricity, with the exception of the Mackenzie River, the longest river in Canada. The Peace, Athabasca and Liard Rivers, as well as Great Bear Lake and Great Slave Lake (respectively the largest and second largest lakes wholly enclosed by Canada) are significant elements of the Arctic watershed. Each of these elements eventually merges with the Mackenzie, thereby draining the vast majority of the Arctic watershed.