Which canal links the Atlantic Ocean to the Great Lakes and opened to deep-draft traffic in 1959?

The canal system that links the Atlantic Ocean to the Great Lakes and opened to deep-draft traffic in 1959 is the St. Lawrence Seaway.

The seaway is a 370-mile network of locks, canals, channels, and navigable sections of the St. Lawrence River. It allows ocean-going ships to travel inland from the Atlantic to the Great Lakes, reaching ports as far west as Duluth, Minnesota, and Superior, Wisconsin. The system crosses the international boundary between Canada and the United States.

Construction began in 1954 after decades of negotiations and engineering proposals. Fifteen locks raise or lower vessels around the rapids and elevation changes between Montreal and Lake Ontario. On April 25, 1959, deep-draft ocean vessels began using the completed route; Queen Elizabeth II, Canadian Prime Minister John Diefenbaker, and U.S. President Dwight Eisenhower formally inaugurated it on June 26.

A common mix-up is the Erie Canal, which connects the Hudson River with Lake Erie but does not provide the direct Atlantic–Great Lakes seaway route. The Welland Canal is part of the Great Lakes navigation system, bypassing Niagara Falls between Lakes Ontario and Erie.