SAINT LAWRENCE RIVER

river of eastern North America, major section of the great hydrographic system stretching 2,500 miles (4,000 km) across the United States and Canada from the source of the St. Louis River in Minnesota through the Great Lakes to the Cabot Strait between Newfoundland and the Canadian mainland. One of the longest rivers in Canada, the St. Lawrence extends approximately 800 miles (1,287 km) from the eastern exit of Lake Ontario through the heartland of the nation to the estuarine Anticosti Island in the Gulf of St. Lawrence. The upper course of the river from Lake Ontario eastward to the city of Cornwall, Ont., forms the border between the United States and Canada. The St. Lawrence flows in a broad tectonic depression and is estuarine over much of its lower course. In its upper and middle courses, the average width is about 1.2 miles (1.9 km), in the lower course about 10 miles (16 km), and at its mouth the river is 90 miles (145 km) wide. The mean discharge rate is about 500,000 cubic feet (14,000 cubic m) per second. The basin of the St. Lawrence covers some 550,000 square miles (1,424,000 square km). The major tributaries of the system include the Ottawa, Saguenay, Richelieu, and Manicouagan rivers, all in Canada. The vegetation in the St. Lawrence basin consists of birch, elm, hemlock, maple, oak, and spruce trees. Sandbank grasses are found along the freshwater river section, and plants with high salt tolerance thrive along the estuarine sections. The St. Lawrence River valley is one of Canada's major agricultural and industrial regions and is noted for dairy products, paper mills, grains, fruits, and timber. A network of hydroelectric-power plants on the river has further accelerated economic growth of the region. The river links the Atlantic Ocean with the Great Lakes through the St. Lawrence Seaway. The major cities on the river are Quebec, Montreal, and Kingston in Canada and Ogdensburg in the United States.