Saint Lawrence, Gulf of, arm of the Atlantic Ocean, c.100,000 sq mi (259,000 sq km), SE Canada, extending c.250 mi (400 km) from the mouth of the Saint Lawrence River to Newfoundland on the east. At its greatest width (northeast-southwest) it is c.500 mi (800 km). It is bounded by Nova Scotia, New Brunswick, and Quebec; in the Gulf are Prince Edward Island, Anticosti Island, the Magdalen Islands, and numerous small islands near its north shore. Chaleur Bay, a west inlet, lies between the Gaspé Peninsula and New Brunswick. The Strait of Belle Isle, Cabot Strait, and the Strait of Canso lead to the Atlantic. The Gulf is subject to frequent fog and is closed to navigation by ice from early December to mid-April. It was visited by explorers before the 16th cent., and it has important fishing grounds, especially for cod.