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The St. Lawrence

The St. Lawrence river system, which includes the Great Lakes, is one of the largest in the world. Ranking third largest in North America after the Mississippi and Mackenzie river systems, the St. Lawrence drains more than 25% of the world's freshwater reserves and shapes the environmental processes of the North American continent.

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The St. Lawrence in Numbers

12 600 m3/s

Average flow at Quebec City

1,6 million km2

Square area

3260 km

Length of river from Lake Superior to Cabot Strait


Global freshwater reserves drained by its hydrographic system


Percentage of the population living along the river’s shores



Fluvial Section, Estuary, and Gulf

The St. Lawrence is much more than just a river; in fact, it has three distinct sections:

 Fluvial SectionEstuaryGulf
Width1 to 5 km40 to 60 km300 km and +
Depth2 to 20 m300 m and +500 m
Water typeFreshwaterBrackishSaltwater

St. Lawrence River

The fluvial section flows from Kingston, Ontario, to Lac Saint-Pierre near Trois-Rivières, Quebec. This section is entirely freshwater and not subjected to tides. It widens in three locations referred to as "fluvial lakes" due to their ecological processes and water flow. These lakes are Saint-François, Saint-Louis and Saint-Pierre.

St. Lawrence Estuary

The St. Lawrence Estuary, point of contact between the river and gulf, which is further subdivided into three zones:

  • a fluvial estuary or freshwater estuary flowing from Lac Saint-Pierre, near Trois-Rivières, as far as the eastern tip of Île d'Orléans in the Québec City area. This zone is subjected to tides. The freshwater flowing into it originates in the Great Lakes and the river's many tributaries.
  • an upper estuary also referred to as a brackish estuary, which runs from the eastern tip of Île d'Orléans to the mouth of the Saguenay River on the North Shore and to the western tip of Île Verte to the south. This is where the freshwater from the river meets the saltwater of the gulf.
  • a lower estuary running between Tadoussac and Pointe-des-Monts, Quebec. This zone is also the starting point of the Laurentian Channel, a very deep natural channel through which dense, nutrient-laden saltwater from the Atlantic Ocean flows.

Gulf of Saint Lawrence

The Gulf of Saint Lawrence, a veritable inland sea, connected to the Atlantic Ocean and bordered by the North Shore (Havre-Saint-Pierre, Sept-Îles, Baie Comeau) and, to the south, the Gaspé Peninsula and the Magdalen Islands with Anticosti Island roughly in the center. Emptying into the Atlantic Ocean, the gulf consists of saltwater.

A Unique Ecosystem

The St. Lawrence is a unique ecosystem constituting a treasure of biological wealth, providing a home to numerous birds, fish and plant species. This ecosystem is recognized worldwide, as reflected in the designation of its four Wetlands of International Importance (RAMSAR), the Lac Saint-Pierre Biosphere Reserve (UNESCO) and its UNESCO World Heritage Site, Miguasha National Park. Along with its coastline and 600 islands, the St. Lawrence has more than 500 protected areas, accounting for 20% of all protected areas in Quebec.

History of St. Lawrence Action Plan