Frequently Asked Soo Locks Questions

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No – both locks operate in both directions and can either raise or lower boats.  The size of the boat determines which lock it will use.  Boats larger than 730 feet long and 76 feet wide are too big for the MacArthur Lock and must use the Poe Lock. 

New Lock construction started in 2020. Phase 1 of construction, deepening the approach channel began in 2020 and was completed August 2022. Phase 2 of construction, rehabilitating the upstream approach walls began in 2021 and is due to be complete summer 2024. Phase 3 of construction, building the new lock chamber was awarded in July 2022 and is scheduled to be complete in 2030.

Boats heading into Lake Superior from the lower Lake Huron Level are described as being ‘upbound’ and will have to be raised up 21 feet at the Locks.  Boats going the other way, from the higher Lake Superior level going towards Lake Huron must be lowered down 21 feet at the Locks and are described as being “downbound.”

Gravity alone moves water in and out of the lock chambers.  Huge culverts run below the lock floors allowing water to flow in or out of the lock depending on which valves are opened.  To raise the level, the emptying valve at the lower end of the lock is closed and the filling valve is opened allowing water to flow into the chamber from the Lake Superior level.  To lower the lock the filling valve is closed and the emptying valve is opened allowing water to flow out to the Lake Huron level. You can check out an animated demonstration of this process.

The water always comes from the higher Lake Superior level. This water continues to flow downward until it eventually reaches the Atlantic Ocean through the St. Lawrence Seaway.

From the time a vessel approaches the lock until the time it leaves takes between 40-60 minutes.  Once the vessel is secured inside the lock it takes 15-20 minutes to raise or lower the boat 21 feet (just over a foot a minute!).

It takes approximately 10 million gallons of water to raise a boat in the MacArthur Lock 21 feet, it takes about 22 million gallons to raise the level of the Poe Lock by 21 feet.

Depending on the size of the boat, yes. The Soo Locks, Welland Canal and St. Lawrence Seaway provide an unbroken water connection between the Great Lakes and the Atlantic Ocean. However, boats larger than 740 feet long and 78 feet wide will not fit through the Welland Canal and can only travel between the four westernmost Great Lakes (Superior, Michigan, Huron and Erie).

Each year, there are between 5,000 to 10,000 passages during the navigation season at the Soo Locks.  

The navigation season at the Soo Locks ends on January 15 and resumes on March 25. During this time, work crews undertake “winter maintenance” doing major repairs, inspections and maintenance projects that cannot be done while the locks are in operation. For winter maintenance updates, check out our Facebook page at:


The largest boat on the Great Lakes is the Paul R. Tregurtha, this boat is 1,014 feet long and 105 feet wide.  (That is longer than three football fields!)

The main cargoes that move through the Soo Locks are taconite (iron ore) and coal going from Western Lake Superior to ports on the lower lakes. Other common cargoes are grain, limestone and salt.  Occasionally, foreign ships bring in windmill parts headed for ports on Lake Superior.

Boats do not pay tolls to use the locks. However, all operation and maintenance (O&M) funding for the locks comes from a tax that cargo vessels pay based on the value of their cargo at their destination port.  These funds go into the Harbor Maintenance Trust Fund (HMTF).  HMTF fully funds all of the O&M on Great Lakes and coastal navigation projects throughout the country. 

To be able to lock through the MacArthur or Poe Lock, a private boat must be motorized (no canoes, kayaks, peddle boats, etc), have 75 feet of line and coordinate with the Chief Lockmaster to receive permission. Private vessel owners should realize there is a set priority hierarchy for use of the locks starting with government vessels, freight vessels, commercial vessels and finally private vessels. During busy times, there could be long waits for the locks and the lockmaster may divert private watercraft to the Canadian Lock on the north shore of the river.

Boats enter the locks under their own power. Most boats registered in the U.S. and Canada have captains and wheelsmen who are fully qualified and licensed to operate on the St. Marys River and through the Soo Locks. Foreign vessels bring on specially licensed Great Lakes Pilots when they enter the waterway and this pilot brings them into the locks.

Crews can vary from shipping company to shipping company, but the typical freighter carries between 22 and 30 crewmembers. They work in either the deck, engine or galley departments on four-hour watches around the clock. Typically they have eight hours off between watches and spend two-four months on board at a time.

The Poe and MacArthur Locks are 32 feet deep “at the sills,” the sills are the highest point within the lock. From the sidewalk to the very bottom of the lock floor is about 65 feet. However, river is maintained to a depth of 28.5 feet.

There is currently one lock on the Canadian side of the river. This lock is 252 feet long by 50.5 feet wide and only 10 feet deep at the sills.

The St. Marys River drops 21 feet within three quarters of mile at the location of the locks. Before the construction of the canals and locks this series of rapids formed a barricade between the upper and lower river. Cargoes traveling down from Lake Superior or up from the lower lakes had to be unloaded and carried around the rapids and then reloaded on different boats to be transported. The construction of the canals and locks allowed vessels to pass around the rapids making transportation both faster and cheaper.

While the Visitor Center is open (May 1 until the end of October), park rangers maintain a boat schedule hotline with estimated arrival times for boats expected at the Soo Locks. Boat arrival times are only known 4-5 hours in advance and all times are estimated. The hotline number is 906-202-1333.

The very first lock on the St. Marys River went into operation in 1797 on the Canadian side of the river. It allowed freight canoes up to 40 feet long to go around the falls without having to unload their goods and be hauled around the rapids. American forces destroyed this lock during  the War of 1812. There would not be another lock at the Sault until 1855 when the State of Michigan opened a lock on the site of the current Poe Lock.

The Poe Lock is the only lock large enough for many of the ships transiting the locks. Nearly all domestically produced high strength steel is made with iron ore that transits the Poe Lock due to the size of ships that carry iron ore. Having an additional lock, the same size as the Poe Lock will allow for better maintenance of both locks and keep traffic moving if the Poe Lock needs unexpected repairs.

 No. The new lock will have the exact same dimensions as the Poe Lock (1200 feet long X 110 feet wide X 32 feet deep). If a bigger lock were constructed, it is likely that bigger boats would quickly follow – recreating the current situation.

It will take 8-10 years, depending on consistent funding and favorable weather. 

Contractors who have gone through the bidding and review process and met strict federal criteria will do most of the work for the new lock. Job inquires with the contractor can be made to Kokosing Alberici Traylor LLC. Jobs with the U.S. Army Corps of Engineers are posted on

Once built, Congress will name the lock. We have no way of knowing what name they will choose.  Earlier locks were named for U.S. Army Corps of Engineers personnel (Weitzel, Poe, Davis, Sabin) or important Army commanders (MacArthur).

The depth of the locks at the sills is 32 feet. Depths in the St. Marys fluctuate quite regularly from a variety of causes. Special gauges throughout the river system monitor water levels and the flow of water through the river. The chief lockmaster monitors these and passes along water depth information to boat captains. If water levels in the river are too low for a vessel to proceed, they will often go to anchor in the upper river, or tie up on the approach piers at the Locks and wait for the water levels to rise. Low water levels throughout the Great Lakes have meant that boats cannot load to their full capacity and therefore have to make more trips and carry less cargo.