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Rivers and Lakes of North America
The great drainage basins of North America are those of streams carrying surface waters from the Interior Plains to the oceans which surround the continent. By far the greatest of the river systems is that of the Mississippi, which gathers its waters from over half the area of the United States and even reaches into western Canada. The arterial stream is the Mississippi itself, which has its source on the swamp-and lake-studded glacial plain in northern Minnesota. From this source, the river follows a tortuous course southward for 2,500 miles (4,023 km) to the Gulf of Mexico. Its greatest tributary from the west is the Missouri, which has a length of 2,700 miles (4,345 km) from its ultimate source in the central Rockies to its junction with the Mississippi.
The greatest tributary from the Eastern Highlands is the Ohio (1,300 miles, 2,092 km, in length), which has its ultimate source at the headwaters of the Allegheny River in Pennsylvania. Spreading like the branches of a tree, this great system has hundreds of other tributaries draining a large part of both the Western and Eastern Highlands and the whole southern half of the Interior Plains. The system has proved both a boon and a tribulation; its broad waters provided routes for early settlement penetration of the interior of the United States and yet, always, the waters have carried the threat of flood.
The northern portion of the Interior Plains is drained northward to the Arctic by the Mackenzie River and its tributaries. The Mackenzie is equal in length, if its farthest head stream is included, to the Mississippi, but it lacks the Mississippi's mighty tributaries. Most of the Mackenzie's tributaries rise in the Canadian Rockies north of the latitude of Edmonton, or on the plains east of the chain of lakes.
The third major drainage line is that of the Great Lakes-St. Lawrence River. The St. Lawrence drains the whole Great Lakes system; the river's ultimate western source is therefore considered to be the source of the St. Louis River in Minnesota.
The Colorado, draining from the central and southern Rockies to the head of the Gulf of California, and the Yukon, draining from the northern Canadian Rockies through central Alaska to Bering Sea, are the other giant water lines upon the continent.
Through the humid East of the United States, there are numerous short, though locally very significant, rivers which drain the flanks of the Eastern Highlands to the Atlantic Ocean, like the Connecticut, the Hudson-Mohawk, the Delaware, the Potomac, and the James. Similarly, in the West, though less numerous and usually shorter, many streams drain the flanks of the Western Highlands to the Pacific Ocean. Only a few of these, like the Snake-Columbia in northwestern United States and adjacent Canada, or the Fraser in southwestern Canada, have cut back into the highland and established large basins.
In the plateau country between the mountain arms of the Western Highlands, there are large areas not drained to the sea. There, the streams are mainly intermittent and their courses lead only to low sections of the plateau surface, where either permanent salt lakes, or salt flats intermittently covered with water, exist.
Lakes are numerous in the northern glaciated portion of North America. By all odds the most significant are the Great Lakes: Superior, Michigan, Huron, Erie, and Ontario. The Lakes are interconnecting and lead into the St. Lawrence River. Superior drains eastward through the St. Mary's River, where falls and rapids made necessary the construction of a canal (the Sault Ste. Marie, or "Soo," Canal) before navigation between Lake Superior and Lake Michigan was possible. This canal ranks with the Suez Canal between the Mediterranean and Red Seas and the Panama Canal between the Caribbean Sea and the Pacific Ocean in shipping tonnage which passes through it.
Michigan and Huron lie at the same level and drain from the south end of Huron through the St. Clair River, Lake St. Clair, and the Detroit River into Lake Erie. Though the level of Erie is below that of Huron, navigation proceeds without the aid of a canal. The Niagara River is the outlet of Lake Erie into Ontario. On this river are the well-known Niagara Falls, circumvented for navigational purposes by the Welland Canal. The giant lake system forms one of the world's most heavily used water highways. With the completion of the St. Lawrence Seaway in 1959, it became fully accessible to direct ocean shipping.