The St. Lawrence Seaway, a series of locks, canals, and channels that allows ships to travel from the Atlantic Ocean to the Great Lakes, was officially opened by British Queen Elizabeth II and U.S. President Dwight Eisenhower on June 26, 1959. Through the seaway, which is known as la Voie Maritime du Saint-Laurent in French, allows ships to go as far as Lake Superior.
Legally, the seaway extends from Montreal to Lake Erie, including the Welland Canal. The seaway is named after the Saint Lawrence River, which it follows from Lake Ontario to the Atlantic Ocean. This section of the seaway is not a continuous canal, but rather comprises stretches of navigable channels within the river, a number of locks, as well as canals made to bypass rapids and dams in the waterway.
The size of vessels that can traverse the seaway is limited by the size of locks. Locks on the St. Lawrence and on the Welland Canal are 766 ft long, 80 ft wide, and 30 ft deep. The maximum allowed vessel size is slightly smaller: 740 ft long, 78 ft wide, and 26.5 ft deep; many vessels designed for use on the Great Lakes following the opening of the seaway were built to the maximum size permissible by the locks, known informally as Seawaymax or Seaway-Max.
Learn about the state of waterways in the United States in the Report Card for America's Infrastructure.