The St. Lawrence River and Seaway is of vital geographic and economic importance to the Great Lakes system, connecting the lakes to the Atlantic Ocean and providing navigation to deep-draft ocean vessels. Approximately 800 miles (1,287 km) long, the St. Lawrence River can be divided into three broad sections: the freshwater river, which extends from Lake Ontario to just outside the city of Quebec; the St. Lawrence estuary, which extends from Quebec to Anticosti Island; and the Gulf of St. Lawrence, which leads into the Atlantic Ocean.