Saint Lawrence River: Seaway Locks, Thousand Islands & Atlantic Inflow

## The Marine Gateway to Continental Fresh Water

The **Saint Lawrence River** (*Fleuve Saint-Laurent*) is the hydrographic outlet of the North American Great Lakes. Flowing **744 miles (1,197 kilometers)** northeast from Lake Ontario to the Gulf of Saint Lawrence, it carves through Quebec, Ontario, and forms the international border with New York State.

### Draining the Great Lakes Basin
Because it drains Lakes Superior, Michigan, Huron, Erie, and Ontario, the St. Lawrence commands a watershed containing roughly **21% of all liquid surface freshwater on Earth**. It has an average volumetric outflow of **346,000 cfs (9,800 m³/s)** at its marine estuary near Tadoussac.

### The Saint Lawrence Seaway Engineering Feat
Completed jointly by the United States and Canada in 1959, the **St. Lawrence Seaway** revolutionized international maritime commerce:
- **System Elevation Lift:** Lifts ocean-going freighters 570 feet (174 meters) from sea level to Lake Erie.
- **Seven Giant Seaway Locks:** Including Snell and Eisenhower locks in New York, and Beauharnois locks in Quebec.
- **The Thousand Islands Region:** A drowned pre-Cambrian crystalline bedrock ridge connecting the Adirondacks to the Canadian Shield.

*Data Source: Saint Lawrence Seaway Development Corporation (SLSDC) & Canadian Hydrographic Service.*