The Saint Lawrence Riveris a large river in the middle latitudes of North America. The Saint Lawrence River flows in a roughly north-easterly direction, connecting the Great Lakes with the Atlantic Ocean and forming the primary drainage outflow of the Great Lakes Basin. It traverses the Canadian provinces of Quebec and Ontario, and is part of the international boundary between Ontario, Canada, and the U.S. state of New York. This river also provides the basis of the commercial Saint Lawrence Seaway.
The St. Lawrence River begins at the outflow of Lake Ontario and flows through Gananoque, Brockville, Morristown, Ogdensburg, Massena, Cornwall, Montreal, Trois-Rivières, and Quebec City before draining into the Gulf of Saint Lawrence, one of the largest estuaries in the world. The estuary begins at the eastern tip of Île d'Orléans, just downstream from Quebec City. The river becomes tidal around Quebec City.
The St. Lawrence River runs 3,058 kilometres from the farthest headwater to the mouth and 1,197 km from the outflow of Lake Ontario. The farthest headwater is the North River in the Mesabi Range at Hibbing, Minnesota.