How Locks Work

Intro Overview Overcoming ObstaclesHow Locks Work

A man throws a cable toward a cargo ship in a lock chamber. The upstream gates of the chamber are shut.

Beauharnois Lock

St. Lawrence Seaway Management Corporation

Locks raise and lower boats in a waterway. By using canals and locks, ships are able to bypass rapids and waterfalls.

The gates of the lock are halfway open. The bridge is raised at a 45-degree angle and the water level in the chamber and in the canal is the same.

Côte Sainte Catherine Lock

St. Lawrence Seaway Management Corporation

The gates of a lock open toward the upstream side. This helps them remain sealed with less effort. In fact, the water upstream can place a great deal of pressure on the gates when the water level in the chamber is lowered.

The gates of the lock are open. The bridge is fully raised and the water level in the chamber and in the canal is the same.

Côte Sainte Catherine Lock

St. Lawrence Seaway Management Corporation

Sometimes a lift bridge is needed to allow a road to pass over a canal.

Photo taken from inside the chamber of a lock with its gates closed. The water level is low and the walls are visible.

Lock on the Soulanges Canal at Pointe-des-Cascades, August 3, 2001

Stratégies Saint-Laurent

The Soulanges Canal was officially opened to navigation on October 9, 1899. Its five locks raised or lowered boats a height of 24 metres between Lake Saint-Louis and Lake Saint Francis. Each lock is 85.3 metres long, 13.7 metres wide and 4.3 metres deep. After the St. Lawrence Seaway was opened in 1959, commercial shipping was rerouted to canals and locks on the South Shore and the Soulanges Canal was closed to navigation. In 1985, it became property of Transports Québec.