Which channel is the world’s longest navigable inland waterway, linking the Great Lakes with the Atlantic Ocean?

The Saint Lawrence Seaway is the navigable waterway linking North America’s Great Lakes with the Atlantic Ocean.

It extends from Montreal to Lake Erie and incorporates the St. Lawrence River, locks, canals, and dredged channels. The modern seaway opened in 1959 after a major Canada–United States construction project, allowing ocean-going ships to reach the Great Lakes.

The seaway is often confused with the Saint Lawrence River, which is the natural river flowing from Lake Ontario toward the Atlantic. It is also distinct from the Welland Canal, a component route that bypasses Niagara Falls between Lake Ontario and Lake Erie.

The system transformed bulk shipping in the Great Lakes region. Vessels known as lakers and ocean-going ships carry grain, iron ore, coal, and other cargo through its locks and channels.