The Soo Locks

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Fishing in the Rapids


Letter from the Secretary of War

Fondly nicknamed by the U.S. Army Corps of Engineers as the "Lynchpin of the Great Lakes," the Soo Locks are an engineering marvel in the adversity of Michigan's water. The locks themselves reflect a national level of increased transportation, industrial, and engineering innovation. Located in Sault Ste. Marie, MI, the Locks hold a crucial position for lake transportation. As shipping and trading expanded in the 1800s, dredging (the act of cleaning out a water bed by scooping out materials with a dredge ["dredge, v.1."]) allowed for an unparalled success between 1870 and 1905. All of the commerce going to and coming from Lake Superior passes through the St. Mary’s Falls Canal. Between the locks and the Detroit River, the two waterways provide a fairly accurate idea of the growth of the commerce upon the whole system. It's estimated that 500,000 people travel to visit the iconic locks annually. 

Before the Soo Locks were built, the Anishinaabe peoples from the area used canoes around the "Bowating" (rapids) to reach Lake Superior from the St. Marie River. As settlement began to increase in the Northwest territories, trade, economy, and methods of cargo shipping followed. Cargo was often portaged around the rapids before any type of lock was constructed. In 1798, the first lock on the St. Mary's River was built to help support the North American fur trade. Situated on the north shore of the river, the lock was approx. 40-ft long and 9-ft wide to accommodate the passage of canoes. The lock carried cargo around the rapids on the Canadian side. During the War of 1812, American forces destroyed the lock and vessels had to once again be unloaded and portaged around the rapids. 

In 1855, the first "State Lock" was built with a state chamber. Owned and operated by the State of Michigan, it was located on the south shore of the river. The project was financed by a congressional land grant of 750,000 acres of public land. This was the first chamber built into the Soo Locks, and transportation between Lake Superior and Lake Huron became possible. By 1881, the Weitzel Lock had opened and the State of Michigan handed over the operation of the lock to the U.S. Corps of Engineers for lack of resources to construct a bigger project, since traffic had increased and vessels had gotten bigger. In 1896, the original Poe Lock was built, named after Orlando Poe. This would be the first lock on the St. Mary's River to use lock gates of steel rather than of wood ("Soo Locks History").

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Map of the St. Mary's River from Lake Superior to Lake Huron


Removing ice from bottom of Poe Lock, April 11, 1907

Since 1883, the locks have gone through at least 6 iterations and been rebuilt with deeper waters and wider margins. The bigger locks sought to accommodate changing ship sizes. While the canoes, at only 40-ft long, were the first vessels, by the 20th century, the shipping industry had grown to allow bigger boats to carry more cargo in fewer trips. The largest freighters now measure 1,000-ft long and 105-ft wide. The current Poe Lock, opened in 1969 to replace the original Poe Lock, was the last lock built in the Soo Locks system, the only passage between Lake Superior and the lower lakes. As part of the Water Recourses Development Act, Congress authorized the largest locks to be built at Sault Ste. Marie. At 1,200-ft long, 110-ft wide and 32-ft deep, the project is expected to take 10 years and cost $600 million dollars. Most of the ships passing through use the Poe Lock. The MacArthur Lock (800 ft), built in 1943, is also still in operation, and as the closest lock to Sault Ste. Marie, the observation deck overlooks this particular lock. 

The Soo Lock's facility, operated and maintained by the U.S. Army Corps of Engineers, Detroit District, is the District’s largest project and is located on the St. Mary's River at Sault Ste. Marie, MI on the international border with Canada. Approximately 80 million tons of commercial commodities pass through the Soo Locks annually (U.S. Army Corp of Engineers). The crews at the Soo Locks complete more than 7000 passages each year during their 42-week season. The locks themselves operate 24/7 to allow travel between Huron and Superior. The shipping season has slowly extended to 10 months since the 19th century due to ice breakers and technological improvements. The locks close in mid-January to late-March. There is a $500.4 billion dollar price tag attributed to the iron ore shipped through the locks each year, and 90% of U.S. Iron Ore passes through the Soo Locks. 


Lower approach to Locks looking west from about 5100 East. Vessels leaving the 3rd lock on October 11, 1915


Two ships in the locks, gates closed with spectators

The CSL Assiniboine passes through the Soo Locks in Sault Ste. Marie, MI

Since 1855, the Soo Locks have functioned as a tourist location. People come to Sault Ste. Marie to watch the boats pass through the locks. In the early days, people would stand on the shore to watch; later, balconies were added for better views. In 1967, a visitor center was built and eventually expanded in 1995. A larger observation platform was installed in 2011. Thanks to the Locks, lake freighters over 1,000 ft can freely pass through the St. Mary's River from Minnesota to the Atlantic Ocean. 

Even with new technological innovation, gravity is still used to move millions of gallons of water to help boats bypass rapids and elevation changes. It takes freighters approximately 9 hours to navigate the 63-mile-long St. Mary’s river at the American Canadian border. From the western most point of the Lake Superior, it is 2,342 miles to the Atlantic Ocean. Despite changes in power and machinery, the locks work as hard as they did 200 years ago, and it still takes 22 million gallons of water to move through the locks.

The Clarke Historical Library houses a collection of images dating from 1885 to 1941 of the construction of the Soo Locks. To view these images, please visit our webpage. These images were obtained in conjuction with the U.S. Army Corps of Engineers in 2016, and 1,731 historic images were able to be digitally preserved thanks to the efforts of the Clarke Historical Library Staff. The original glass plate negatives were held by the U.S. Army Corps of Engineers at the Soo Area Office from their creation until July, 2016. The negatives cans now be found at the Still Pictures Unit of the National Archives and Records Administration (NARA) in College Park, Maryland. The Soo Locks were designated a National Historic Landmark in 1966. 

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