The Soo Locks (sometimes spelled Sault Locks but pronounced "soo") are a set of parallel
locks, operated and maintained by the
United States Army Corps of Engineers, Detroit District, that enable
ships to travel between
Lake Superior and the lower
Great Lakes. They are located on the
St. Marys River between Lake Superior and
Lake Huron, between the
Upper Peninsula of the
U.S. state of
Michigan and the
Canadian province of
Ontario. They bypass the rapids of the river, where the water falls 21 ft (6.4 m). The locks pass an average of 10,000 ships per year,[4] despite being closed during the winter from January through March, when ice shuts down shipping on the Great Lakes. The winter closure period is used to inspect and maintain the locks.
The locks share a name (usually shortened and anglicized as Soo) with the two cities named Sault Ste. Marie,
in Ontario and
in Michigan, located on either side of the St. Marys River. The
Sault Ste. Marie International Bridge between the United States and Canada permits vehicular traffic to pass over the locks. A railroad bridge crosses the St. Marys River just upstream of the highway bridge.
The first locks were opened in 1855. Along with the
Erie Canal, constructed in 1824 in central New York State, they were among the great infrastructure engineering projects of the antebellum United States. The Soo Locks were designated a
National Historic Landmark in 1966.[5]
During World War II, the Soo Locks and the St. Marys River waterway were intensely guarded by U.S. and Canadian forces coordinated by the
U.S. Army's
Central Defense Command, as they were considered integral to continued shipping traffic on the Lakes. A one-way German air attack on the locks by forces based in Norway was thought to be possible.[6]
United States locks
The U.S. locks form part of a 1.6 mi (2.6 km) canal formally named the St. Marys Falls Canal. The entire canal, including the locks, is owned and maintained by the
United States Army Corps of Engineers, which provides free passage. The first iteration of the U.S. Soo Locks was completed in May 1855; it was operated by the state of Michigan until transferred to the U.S. Army in 1881.
The first federal lock, the Weitzel Lock, was built in 1881 and was replaced by the MacArthur Lock in 1943.[7][8] The configuration consists of two parallel lock chambers, each running east to west. Starting at the Michigan shoreline and moving north toward Ontario, these are:
The MacArthur Lock, built in 1943. It is 800 ft (240 m) long, 80 ft (24 m) wide, and 29.5 ft (9.0 m) deep.[9] This is large enough to handle ocean-going vessels ("salties") that must also pass through the smaller locks in the
Welland Canal. The first vessel through was the
SS Carl D. Bradley.
The Poe Lock, built in 1896. The first vessel to pass through was the U.S. Army Corps of Engineers tug USS Hancock.[10] The original Poe Lock was engineered by
Orlando Poe and, at 800 ft (240 m) long and 100 ft (30 m) wide, was the largest in the world when completed in 1896.[11] The lock was re-built in 1968 to accommodate larger ships, after the
Saint Lawrence Seaway opened and made passage of such ships possible to the Great Lakes. It is now 1,200 ft (370 m) long, 110 ft (34 m) wide, and 32 ft (9.8 m) deep.[9] It can take ships carrying 72,000 short tons (65,000 t) of cargo. The Poe is the only lock that can handle the large
lake freighters used on the Upper Lakes. The first passage after the rebuild was by the Phillip R. Clarke in 1969.[11]
A new lock is under construction and is slated to be completed by 2030.[12] Groundbreaking for the new lock project was held on June 30, 2009.[13] The lock will be equal in size to the Poe Lock and will provide much needed additional capacity for the large lake freighters.[14] The new lock replaces two locks (Davis Lock and Sabin Lock), which were obsolete and used infrequently. In May 2020, construction on Phase One of the replacement of the Sabin Lock was started.
North of the new lock is an additional channel with a small hydroelectric plant, which provides electricity for the lock complex.
MacArthur Lock, facing north
Engineers Day
The U.S. Army Corps of Engineers, Detroit District, operates the Soo Locks Visitors Center and viewing deck for the public.[15] On the last Friday of every June, the public is allowed to go behind the security fence and cross the lock gates of the U.S. Soo Locks for the annual Engineers Day Open House.[16][17] During this event, visitors are able to get close enough to touch ships passing through the two regularly operating locks. Other than on that day, because the locks are United States Federal property under command of the U.S. Army Corps of Engineers, unauthorized personnel and civilians are restricted from the locks under threat of fines or imprisonment for trespassing.
A single small lock is operated on the Canadian side of the Soo. Opened in 1895, it was rebuilt in 1987, and is 77 m (253 ft) long, 15.4 m (51 ft) wide and 13.5 m (44 ft) deep.[18] The Canadian lock is used for recreational and tour boats; major shipping traffic uses the U.S. locks.
^"St. Marys Falls Canal". National Historic Landmark summary listing. National Park Service. Archived from
the original on October 6, 2012. Retrieved June 27, 2008.
^Conn, Stetson; Engelman, Rose C.; Fairchild, Byron (2000) [1964].
Guarding the United States and its Outposts. United States Army in World War II. Washington, D.C.: Center of Military History, United States Army. pp. 102–105.
Archived from the original on December 25, 2007. Retrieved June 14, 2018.
^Saint Marys Falls Ship Canal (Soo Locks Historic District, Soo Canals), Michigan Department of Labor and Economic Opportunity, 2020.
^"Chapter 4: The Watery Boundary". United Divide: A Linear Portrait of the USA/Canada Border. The Center for Land Use Interpretation. Winter 2015.
Archived from the original on June 20, 2018. Retrieved November 14, 2017.