Locks of the Montreal – Lake Ontario Section of the Seaway prior to 1901

Locks of the Montreal Lake Ontario Section of the Seaway prior to 1901

Source: adapted from J. Gilmore (1957) “The St. Lawrence River Canals Vessel”, Society of Naval Architects and Marine Engineers, Transactions, 1957, pp. 111-161.

The St. Lawrence River, between Montreal and Kingston, is composed of a series of rapids, impending navigation, and fluvial lakes. Prior to 1780, the only way to bypass the rapids was through portages, which substantially limited the commercial potential of the route. Canoes were the privileged mode of transportation in the 18th century as they could easily be carried across rapids, but their payload was limited. By the late 18th and early 19th century, they were replaced by bateaux of 35-40 feet in length, 6 feet in width, and a cargo capacity of 3.5 tons. They could also be portaged or towed upstream and were also able to cross some rapids going downstream. Yet, this was insufficient to support the growing trade relations with the fast-developing regions of Southern Ontario.

In order to have access to the Great Lakes, a set of locks and canals were built between 1785 and 1901. The canals and locks permitted to bypass the rapids between Lake St. Louis and Lake St. Francois in 1785, but the locks’ size were modest (40 feet long by 6 feet wide and a depth of 2 and a half feet). As the system evolved, the capacity and reliability of canals improved. The completion of the Lachine Canal in 1825 is an important landmark as a major navigational constraint, to which Montreal owns its location, was finally bypassed. In 1848, with the completion of the Beauharnois Canal and a series of locks bypassing the International Rapids between Lake St. Francis and Prescott at the tip of Lake Ontario, portages were finally no longer required. By 1901, with the expansion of the locks forming the Williamsburg Canals and the completion of the Soulanges Canal, which was of higher capacity than the old Beauharnois Canal, it was possible to go from Montreal to Prescott through a 4.25 meters (14 feet) deep canal system. These dimensions would remain until the St. Lawrence Seaway was completed in 1959.