Rivière des Prairies

Dusk over Île de la Visitation and the Pont Papineau-Leblanc, Rivière des Prairies

The Rivière des Prairies (sometimes called the Back River in English) is a channel of the Saint Lawrence River in southwestern Quebec, Canada.

Flowing west to east, it rises in the Lac des Deux-Montagnes. It divides the Island of Montreal (Montreal) to the south from Île Jésus (Laval and Île Bizard (part of Montreal) to the north, and rejoins the Saint Lawrence at the eastern tip of the Island of Montreal.

The river contains a large number of islands, including the Îles Laval (Île Bigras, Île Pariseau, Île Verte and Île Ronde) belonging to Laval, and Île de la Visitation, a nature park belonging to Montreal. The Rapides du Cheval Blanc occur downstream from the Îles Laval, in the portion of the river dividing the district of Pierrefonds in Montreal from Sainte-Dorothée in Laval.

Historically, the river received massive discharges of untreated liquid waste from Montreal, turning it into essentially an open sewer; however, ecological intervention and modern treatment techniques reversed the damage and the river is now considered clean.