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.
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
25%
Global freshwater reserves drained by its hydrographic system
60%
Percentage of the population living along the river’s shores
244
Tributaries
Fluvial Section, Estuary, and Gulf
The St. Lawrence is much more than just a river; in fact, it has three distinct sections:
| Fluvial Section | Estuary | Gulf | |
| Width | 1 to 5 km | 40 to 60 km | 300 km and + |
| Depth | 2 to 20 m | 300 m and + | 500 m |
| Water type | Freshwater | Brackish | Saltwater |
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.
