Montmorency, << `mont` muh REHN see, >> River is a short, swift river in Quebec. It is named for the Duc de Montmorency, an admiral of France. The river rises in Snow Lake and flows southward for about 62 miles (100 kilometers). It empties into the Saint Lawrence River about 6 miles (10 kilometers) northeast of Quebec City. Montmorency Falls, which are about 150 feet (46 meters) wide and 251 feet (77 meters) high, lie at the mouth of the river. They are Quebec’s highest waterfall.