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.
Drainage basin
Because drainage basins are coherent entities in a hydro-logical sense, it has become common to manage water resources on the basis of individual basins. In the U.S. state of Minnesota, governmental entities that perform this function are called "watershed districts". In New Zealand, they are called catchment boards. Comparable community groups based in Ontario, Canada, are called conservation authorities. In North America, this function is referred to as "watershed management".
In Brazil, the National Policy of Water Resources, regulated by Act n° 9.433 of 1997, establishes the drainage basin as the territorial division of Brazilian water management.