Named "le fleuve Saint-Laurent" (French for "The Saint Lawrence River") by its discoverer, explorer Jacques Cartier (click here for video), who was looking for the Northwest Passage, this river is a very important trade route shared between the United States and Canada.
The water of all 5 lakes of the Great Lakes flows out through the St. Lawrence River. The river begins in Lake Ontario on the U.S./Canada border. It flows northeast, continuing only into Canada, where it gets wider. It empties into the Gulf of St. Lawrence, which is part of the Atlantic Ocean.