The Great Lakes-St. Lawrence Seaway system is a “marine highway” that extends from the Atlantic Ocean to the Great Lakes.
The Great Lakes-St. Lawrence Seaway was built as a binational partnership between the U.S. and Canada, and continues to operate as such.
Administration of the system is shared by two entities, Great Lakes St. Lawrence Seaway Development Corporation in the U.S., and The St. Lawrence Seaway Management Corporation in Canada, a not-for-profit corporation (ownership of the Canadian portion of the Seaway remains with the Canadian federal government.)
Construction of the St. Lawrence Seaway between Montreal and Lake Ontario during the mid to late 1950s has been recognized as one of the most challenging engineering feats in history.
A total of seven locks were built, five Canadian and two U.S., in order to lift vessels 246 feet (75 meters) above sea level as they transit from Montreal to Lake Ontario.
Combined with the eight locks of the Welland Canal, which link Lake Ontario to Lake Erie, the binational St. Lawrence Seaway’s 15 locks (13 Canadian and 2 American) allow ships to transit between Montreal and Lake Erie, a difference in elevation of 551 feet (168 meters).
Locks on the St. Lawrence Seaway and Welland Canal are 766 ft (233.5 m) long, 80 ft (24.4 m) wide, and 30 ft (9.14 m) deep.
The maximum allowed vessel size is slightly smaller: 740 ft (225.6 m) long, 78 ft (23.8 m) wide, and 26.5 ft (8.1 m) deep.
A ship transiting the Seaway System’s 15 locks from Montreal to Lake Erie crosses the international border 27 times.
In Sault Ste. Marie on the St. Marys River, the Soo Locks enable ships to reach Lake Superior. The locks are managed by the U.S. Army Corps of Engineers.
Lake Superior is the western terminus of the St. Lawrence Seaway System. The Port of Thunder Bay is the westernmost Canadian port. The Port of Duluth-Superior (Duluth, Minnesota, and Superior, Wisconsin) is the westernmost U.S. port.