Coteau-du-Lac Canal

Coteau-du-Lac Canal is an 18th Century military canal in Canada located at the junction of the Delisle and Saint Lawrence Rivers in Quebec. The canal was the first work of its kind in North America, and is a National Historic Site of Canada. It is located in the town of Coteau-du-Lac in Vaudreuil-Soulanges Regional County Municipality, Quebec.

The American War of Independence (1775–1783) revealed a number of serious flaws in the British defence system. The western frontier of the Canadian colony was protected by the military outposts on the Great Lakes. However, these outposts were all the more vulnerable for being difficult to reach. Troop and merchandise transport via the Saint Lawrence River was seriously slowed by the rapids located upstream from Montreal. In particular, the rapids at Coteau-du-Lac were the most difficult to get past and skirting the rapids by going inland prolonged supply times. To accelerate shipment of military supplies westward, Governor Frederick Haldimand ordered for a canal to be dug at Coteau-du-Lac.

The construction of the canal at Coteau-du-Lac began in 1779 under the control of Captain William Twiss. The King's Royal Regiment of New York were mobilised to dig the canal.

When construction was completed On February 15, 1781, the lock system was approximately 100 metres long and 2.5 metres wide. Each of the three locks was 12 m long and 1.8 m wide, with draft measuring close to 80 cm. Taken together, these locks compensated for a drop of about 2 m between the head and the bottom of the rapids.

Today, water no longer flows around the site or through the canal owing to a drop in water levels due to the building of hydroelectric dams, the building of newer dams, and other modern development.