The St. Lawrence River Estuary is an estuary at the mouth of the St. Lawrence River. It stretches 655 km from west to east, from the outlet of Lake Saint Pierre to Pointe-des-Monts, where it becomes the Gulf of St. Lawrence, in Quebec, Canada.
The estuary is divided into 3 parts: the fluvial estuary, the middle estuary and the maritime estuary. The waters coming from the north shore of the St. Lawrence and Labrador come mainly from the Canadian Shield.