The Rivière des Mille Îles ("River of the Thousand Islands") is a channel of the Ottawa River (Lake of Two Mountains) in southwestern Quebec, Canada and runs into the Rivière des Prairies.
It divides Île Jésus (the city of Laval) from the North Shore, the northern mainland suburbs of Montreal (such municipalities as Deux-Montagnes, Saint-Eustache, Boisbriand, Rosemère, Lorraine, Bois-des-Filion, Sainte-Thérèse, and Terrebonne.)
The river rises at the narrowing of the Lac des Deux Montagnes and flows west to east. It joins the Rivière des Prairies at the eastern tip of Île Jésus, which shortly thereafter joins the St. Lawrence at the eastern tip of the Island of Montreal.
As its name suggests, the river contains many small islands which are part of the Hochelaga Archipelago. It is not to be confused with the Thousand Islands at the head of the St. Lawrence River, in Ontario and New York State.