The Estuary and the Gulf of St. Lawrence
The St. Lawrence River begins as the outflow of the Great Lakes and widens into a large estuary near Ile d’Orléans, where the river’s fresh water first encounters oceanic salt water and where the typical two-layer estuarine circulation begins. Continuing downstream, the surface water of the St. Lawrence becomes more and more salty, finally having a true oceanic character at the head of the Laurentian Channel (off-shore of Tadoussac), where strong upwellings bring deep waters to the surface.
Among the deepest and largest estuaries in the world, the St. Lawrence maritime estuary extends nearly 250 km before it widens at Point-des-Monts into the Gulf of St. Lawrence. This enclosed sea is connected to the Atlantic Ocean by Cabot Strait and the Strait of Belle-Isle.