A river of southeast Canada flowing about 1,207 km (750 mi) northeast from Lake Ontario along the Ontario-New York border and through southern Quebec to the Gulf of St. Lawrence. The river was first sighted by Jacques Cartier in 1534; in 1535 he ascended it as far as the site of the modern-day city of Montreal. Long a water highway for explorers, missionaries, and fur traders, it is today a major shipping route. River, southern Quebec and southeastern Ontario, Canada. It flows northeast out of Lake Ontario into the Gulf of Saint Lawrence and is about 760 mi (1,225 km) long. It passes through the Thousand Islands and for about 120 mi (195 km) forms the boundary between New York and Ontario. Entering Quebec, it widens into Lake St. Francis, then flows past Montreal island. Below Quebec city it widens to 90 mi (145 km) at its mouth in the Gulf of St. Lawrence. Major tributaries include the Ottawa, Saguenay, Richelieu, and Manicouagan rivers, all in Canada. It links the Atlantic Ocean with the Great Lakes through the Saint Lawrence Seaway
{i} river flowing west-to-east in North America (the river bisects the Canadian province of Quebec and forms part of the border between the state of New York in the United States and the province of Ontario in Canada)