The rivière Saint-Charles is a tributary of the south shore of the Saint Lawrence River, flowing in the city of Varennes, in the Marguerite-D'Youville Regional County Municipality, in the administrative region of Montérégie, southwest of province of Quebec, to Canada. The lower course of the Saint-Charles river more or less delimits the urban part of Varennes passing on the south side. The intermediate and upper parts flow in agricultural area.