The rivière des Aulnaies (English: alders river) is a tributary of the rivière du Milieu, flowing on the west side of the Saint-Maurice River, in the Matawinie Regional County Municipality, in the administrative region of Lanaudière, in the province of Quebec, in Canada.

The river surface is generally frozen from mid-December until the end of March.

The Aulnaies River rises at the mouth of Carufel Lake (length: 0.8 km (0.50 mi); altitude: 438 m (1,437 ft)) in the township of Brassard, in the municipality of Saint -Michel-des-Saints.

This lake is located on the southwest side of a mountain whose summit reaches 573 m (1,880 ft).

The confluence of the Aulnaies river is located at: The toponym Rivière des Aulnaies was formalized on December 5, 1968, at the Commission de toponymie du Québec.