The St. Lawrence River: Great Lakes Gateway to the Atlantic

The St. Lawrence River is the primary hydrological outlet of the Great Lakes system, connecting the world's largest freshwater lake complex to the Atlantic Ocean.

The Connection

• Source: Flows out of Lake Ontario at Kingston, Ontario.
• Course: Runs northeast ~1,197 km (744 mi), forming part of the Canada–USA border (Ontario/Quebec vs. New York).
• Key Feature: Passes through the Thousand Islands region.
• Mouth: Widens into the Gulf of St. Lawrence (the world's largest estuary) before entering the North Atlantic off Newfoundland.

Economic & Strategic Importance

The St. Lawrence Seaway (a system of locks, canals, and channels completed in 1959) allows ocean-going vessels to sail from the Atlantic to Lake Superior—over 3,700 km (2,300 mi) inland. This enables direct shipping of grain, iron ore, coal, and manufactured goods between the North American heartland and global markets, making it one of the world's most vital commercial waterways.