Soo Locks: The 21-Foot Step That Connects Lake Superior, Michigan

Lake Superior is the highest of the Great Lakes, and it has only one outlet: the St. Marys River. Where the river leaves the lake at Sault Ste. Marie, it drops about 21 feet over three-quarters of a mile of rapids and hard sandstone. For centuries, that drop was a wall. Boats could not go up or down it. Cargo had to be unloaded, carried around the rapids, and loaded onto other boats. In the 1840s, copper and iron ore were discovered in Michigan's Upper Peninsula, and suddenly that wall mattered. Some in Congress thought a canal at such a remote place was absurd. One senator compared it to building a canal on the moon. But in 1853 the State of Michigan went ahead. Crews working in brutal conditions cut through solid rock, and in 1855 the first locks opened: two chambers in tandem, each 350 feet long, at a cost nearly three times the estimate. In June 1855, the first steamer passed through, and for the first time ships could sail freely between Lake Superior and the lower lakes. In 1881, the federal government took over, and the U.S. Army Corps of Engineers has run the locks ever since. Passage has always been free. As ships grew, the locks grew with them. The MacArthur Lock opened in 1943, and it's 800 feet long. The Poe Lock, first built in 1896, was rebuilt and reopened in 1968 at 1,200 feet long and 110 feet wide. It's the only lock at the Soo big enough for the 1,000-foot freighters that carry iron ore across the lakes. Each time the Poe fills or drains to raise or lower a ship those 21 feet, it moves up to 22 million gallons of water, using nothing but valves and gravity. That makes the Poe a single point of failure for American industry. According to the Army Corps of Engineers, 88% of all U.S. domestic iron ore shipping depends on it. If it were shut down, much of the Great Lakes fleet would be stuck. So a second lock the same size is being built. Construction began in 2019 on the site of two old, outdated locks. The project is estimated at $3.2 billion and is on schedule for completion in 2030. The Soo Locks were designated a National Historic Landmark in 1966, and they're still one of the busiest working waterways in the country.