Color postcard from 1930 of crowds of people lining the Davis Lock, watching ships move through it, in Sault Sainte Marie, Michigan. The postcard is part of a Sault Sainte Marie souvenir postcard booklet. The Soo Locks, located on St. Marys River between the United States and Canada, provide ships safe passage around the rapids in the canal. The first locks in this canal were built in 1855, and have been improved upon ever since. The locks are the busiest, based on tonnage passing through, in the world. The Davis Lock, built in 1914, with the Sabin Lock (1919), are incredibly long, at 1350 feet (compared to the 800 foot Poe and MacArthur Locks).