The Mille-Îles River is over 42 km long. It allows the Ottawa River and the Lake des Deux-Montagnes to flow into the St. Lawrence. The Abenaki named it Makigôteckw River. Near Île-des-Moulins, there's a sanctuary where it is possible to observe more than two hundred different species of birds. Ducks, Canada geese and great blue herons are just a few you can see during the year.
Many activities are offered on the Mille-Îles River: kayaking, canoeing, rabaska, pedal boats, etc. A rowing club offers departures at Parc de la rivière in Terrebonne and Groupe Plein Air Terrebonne offers rentals of various types of boats. The Mille-Îles River is also crossed by La Route Bleue, a navigable route of 155 km, starting on the Ottawa River and ending near Repentigny.