The Saint Lawrence Seaway officially opened to ocean-going traffic in 1959.
Queen Elizabeth II and U.S. President Dwight D. Eisenhower formally opened the waterway on 26 June 1959. The project created a navigable route from the Atlantic Ocean through the Saint Lawrence River to the Great Lakes, allowing ocean-going vessels to reach ports as far inland as Lake Superior.
Construction involved canals, locks, dredging, and the creation of the Moses–Saunders Power Dam. Several communities and historic sites were relocated or submerged during the development of the seaway and associated St. Lawrence Power Project.
The seaway did not make every part of the Great Lakes accessible to ships of any size. Vessels must fit the dimensions of its locks and channels, giving rise to the term “Seawaymax.” The waterway remains a major route for grain, iron ore, coal, and other bulk cargo.