St. Lawrence River

The St. Lawrence River, known in French as the Fleuve Saint-Laurent, is a major international waterway in North America that links the Great Lakes to the North Atlantic Ocean. Flowing northeast from Lake Ontario, it passes through the Canadian provinces of Ontario and Quebec, as well as the U.S. state of New York, with a section of its course forming part of the Canada–United States border. As the main outlet for the Great Lakes Basin, it ranks second among North American rivers in discharge volume—only the Mississippi River carries more water—and sixteenth globally. Scientists frequently describe its estuary as the largest in the world.

The river has long served as a transportation route for Indigenous peoples and played a central role in Canadian history, particularly in the growth of Montreal and Quebec City. Today, it remains a vital shipping corridor, forming the core of the St. Lawrence Seaway, a system of locks and canals that allows ocean-going vessels to reach inland ports on the Great Lakes Waterway. Notable natural features along its course include the 1,864 islands of the Thousand Islands, the endangered whale population of the Saguenay–St. Lawrence Marine Park, and the limestone monoliths of the Mingan Archipelago. Over time, the river has carried many names from local First Nations.

Etymology

In the 16th century, French explorers arriving in what is now Canada called it the Grand fleuve de Hochelaga and the Grande rivière du Canada—using fleuve for a river that empties into the sea. The modern name dates to 1604, when Samuel de Champlain recorded it on a map, choosing Grande riviere de sainct Laurens and Fleuve sainct Laurens in his writings, which replaced earlier terms. In contemporary French, it is the fleuve Saint-Laurent.

Marine weather

Jacques Cartier originally applied the name Saint-Laurent to the bay after arriving on August 10, 1535, the feast day of Saint Lawrence. Indigenous names include: in Innu-aimun, Wepistukujaw Sipo or Wepìstùkwiyaht sīpu; in Abenaki, Moliantegok or Moliantekw (“Montréal River”), Kchitegw or Ktsitekw or Gicitegw (“Great River”), or Oss8genaizibo or Ws8genaisibo or Wsogenaisibo (“River of the Algonquins”); in Mohawk, Roiatatokenti, Raoteniateara, Ken'tarókwen, or Kaniatarowanénhne; in Tuscarora, Kahnawáˀkye or Kaniatarowanenneh (“Big Water Current”); in Algonquin, “the Walking Path” or Magtogoek, or Kitcikanii sipi (“Large Water River”); in Wendat, Lada8anna or Laooendaooena'; and in Atikamekw, Micta sipi (“Huge River”). During winter, ice begins forming on the St. Lawrence between Montreal and Quebec City in December. Prevailing winds and currents push this ice toward the estuary, reaching east of Les Méchins by the end of the month.

By January and February, ice covers the entire Gulf of St. Lawrence. This ice aids navigation by suppressing wave formation and spray, which helps prevent ships from icing over. The river formed as the Champlain Sea drained away, a process driven by the rebounding continent after the Last Glacial Maximum. That sea existed from roughly 13,000 to 10,000 years ago, shrinking continuously—a trend that persists today.

Watershed

Near its head at Lake Ontario lies the Thousand Islands region. The St. Lawrence now begins at Lake Ontario’s outflow, flowing past Cape Vincent, Gananoque, Clayton, Alexandria Bay, Brockville, Morristown, Ogdensburg, Massena, Cornwall, Montreal, Trois-Rivières, and Quebec City before emptying into the Gulf of St. Lawrence, often considered the world’s largest estuary. The estuary starts at the eastern tip of Île d’Orléans, just downstream from Quebec City, and the river becomes tidal around that city.

From its farthest headwater—the North River in Minnesota’s Mesabi Range near Hibbing—to its mouth, the river runs 3,058 kilometers (1,900 miles). From Lake Ontario’s outflow, it measures 1,197 kilometers (743.78 miles) including the estuary, or 500 kilometers (311 miles) without it. Its drainage basin, which includes the Great Lakes—the largest system of freshwater lakes on Earth—covers 1,344,200 square kilometers (518,998.5 square miles), with 839,200 km² (324,016.9 sq mi) in Canada and 194,981.6 square miles (505,000 km²) in the United States. This basin spans parts of Ontario and Quebec in Canada, and parts of Minnesota, Wisconsin, Illinois, Indiana, Ohio, Pennsylvania, New York, Vermont, and nearly all of Michigan in the U.S. Average discharge below the Saguenay River is 16,800 cubic meters per second (590,000 cu ft/s); at Quebec City, it is 12,101 m³/s (427,300 cu ft/s); and at the source (Lake Ontario’s outflow), it is 7,410 m³/s (262,000 cu ft/s).

The river includes Lake Saint Francis near Salaberry-de-Valleyfield, Lake Saint-Louis south of Montreal, and Lake Saint Pierre east of Montreal. It also contains four archipelagoes: the Thousand Islands near Alexandria Bay, New York, and Kingston, Ontario; the Hochelaga Archipelago (including Montreal Island and Île Jésus, or Laval); the Lake St. Pierre Archipelago (designated a UNESCO biosphere world reserve in 2000); and the smaller Mingan Archipelago. Other islands include Île d’Orléans near Quebec City and Anticosti Island north of the Gaspé. It is Canada’s second-longest river.