Lake Mégantic () is a body of water in Québec, located in the Appalachian Mountains near the U.S. border. It is a source of the Chaudière River which drains into the St Lawrence River at Québec City. The lake has a surface area of with several villages and small towns on its shores, including Lac-Mégantic, Frontenac, Marston, and Piopolis. It is part of Le Granit Regional County Municipality, a rural region where forestry and granite extraction are important activities.