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.
Kootenay River
The Columbia Basin is noted for its spring floods, major flood years were 1876, 1894, 1948 and 1964. As recently as the mid-1960s, the upper Columbia and Kootenay rivers in British Columbia were still free-flowing and unaffected by dams and reservoirs, resulting in the 1948 Vanport Oregon flood. The uncontrolled discharge past the Canada-U.S. border created problems for electricity generation in the US, and Canada also wanted to utilize the Columbia river for the production of hydroelectric power. Negotiated in 1961 between the governments of the two countries, the Columbia River Treaty attempted to ratify these problems. Construction of the first three of the four dams authorized by the treaty—Mica, Keenleyside and Duncan—was implemented in 1964. Of the four dams, the first two are on the Columbia, the third is on the Duncan River, a tributary of the Kootenay, and the fourth Libby, on the Kootenay River proper. However, operation of the dams has led to environmental problems in both rivers because they have caused unnatural flow fluctuations, blocked fish migration, flooded fertile agricultural land, and forced over 2,000 people to relocate.