Utilizing lock infrastructure, vessels are able to overcome changes in waterway elevation. On the Great Lakes Seaway system, 16 locks lift or lower ships a total of 600 feet from Montreal to Lake Superior.

Ships reach Lake Superior from the Atlantic Ocean via the Great Lakes St. Lawrence Seaway system, a massive engineering feat. The journey begins by traveling up the St. Lawrence River through a series of seven locks between Montreal and Lake Ontario. To bypass Niagara Falls, ships enter the Welland Canal, which uses eight locks to lift vessels over 300 feet from Lake Ontario to Lake Erie. From there, they sail through Lake Huron to reach the final hurdle: the Soo Locks at Sault Ste. Marie. Because Lake Superior is about 20 feet higher than Lake Huron, the Soo Locks (specifically the Poe and MacArthur locks) act as a "water elevator," lifting these massive 1,000-foot "Lakers" or smaller ocean-going "Salties" into the largest of the Great Lakes. In 2026, this system remains a vital artery for the transport of iron ore, grain, and coal, despite the winter freeze which typically shuts down the locks from January to March for essential maintenance.