Grand lac Saint-François is a sprawling freshwater lake covering 51 square kilometres (approximately 12,486 acres) in southeastern Quebec, Canada, straddling the Les Appalaches and Le Granit regional county municipalities. Situated southeast of Thetford Mines in the Appalachian region, this impressive body of water holds the distinction of being the third largest lake south of the St. Lawrence River. It serves as the headwater source of the Saint-François River, lending it significant ecological importance in the region. Partially encompassed within Parc national de Frontenac, the lake offers a remarkable combination of natural beauty, expansive open water, and diverse fishing opportunities that draw anglers from across Quebec and beyond. With a shoreline stretching over 76 miles, there is no shortage of water to explore, and the lake's setting among the rolling Appalachian landscape makes it as scenic as it is productive.