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 southern parts of Quebec and Ontario, in the section of the Great Lakes (bordered entirely by Ontario on the Canadian side) and St. Lawrence basin (often called St. Lawrence Lowlands), is another particularly rich sedimentary plain. Prior to its colonization and heavy urban sprawl of the 20th century, this Eastern Great Lakes lowland forests area was home to large mixed forests covering a mostly flat area of land between the Appalachian Mountains and the Canadian Shield. Most of this forest has been cut down through agriculture and logging operations, but the remaining forests are for the most part heavily protected. In this part of Canada the Gulf of St. Lawrence is one of the world's largest estuary (see Gulf of St. Lawrence lowland forests).