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 Canadian Rockies are part of a major continental divide that extends north and south through western North America and western South America. The Columbia and the Fraser Rivers have their headwaters in the Canadian Rockies and are the second and third largest rivers respectively to drain to the west coast of North America. To the west of their headwaters, across the Rocky Mountain Trench, is a second belt of mountains, the Columbia Mountains, comprising the Selkirk, Purcell, Monashee and Cariboo Mountains sub-ranges.