The Assomption River (in French "", named after the Assumption of Mary) is the most important waterway in the Lanaudière region of Quebec, Canada. It is over long. It has a drainage basin of . It flows from the Mont Tremblant massif. Seven significant rivers flow into the Assomption (de la Boule, Versailles, Noire, la Chaloupe, Ouareau, Saint-Esprit, and Achigan) before it flows into the Rivière des Prairies at Repentigny, Quebec.