The Gulf of Saint Lawrence is the world's largest estuary. It is the outlet of the Saint Lawrence River into the Atlantic Ocean.
The river flows into the gulf through the Jacques Cartier Strait between the Côte-Nord region of Quebec and Anticosti Island, and the Honguedo Strait between Anticosti Island and the Gaspé Peninsula.
The gulf is bounded on the north by the Labrador Peninsula, to the east by Newfoundland, to the south by Nova Scotia (particularly Cape Breton Island), and to the east by the Gaspé and New Brunswick. It contains Anticosti Island, Prince Edward Island, and the Magdalen Islands.
Besides the Saint Lawrence River itself, tributaries of the Gulf of Saint Lawrence include the Miramichi River, the Natashquan River, and the Matapédia River; arms of the Gulf include the Baie des Chaleurs, the Miramichi River estuary, St. George's Bay, and Northumberland Strait.