Lac Saint-Jean is a large, relatively shallow lake in south-central Quebec, Canada, in the Laurentian Highlands. It is situated 206 km (128 mi) north of the Saint Lawrence River, into which it drains via the Saguenay River. It covers an area of 1,053 km2 (407 sq mi), and is 63 m (207 ft) at its deepest point. Its name in the Innu language is Piekuakamu.
The lake is fed by dozens of small rivers, including the Ashuapmushuan, the Mistassini, the Peribonka, the Des Aulnaies, the Métabetchouane, and the Ouiatchouane.
The towns on its shores include Alma, Dolbeau-Mistassini, Roberval, Normandin, and Saint-Félicien.
Three Regional County Municipalities lie on its shores: Lac-Saint-Jean-Est, Le Domaine-du-Roy, and Maria-Chapdelaine.
