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 63.1 m (207 ft) at its deepest point. Its name in the Innu language is Piekuakamu.

The Metabetchouan River is a tributary of Lac Saint-Jean in the centre of the province of Quebec, Canada. The course of this river successively crosses the regional county municipalities (MRC) of:La Jacques-Cartier Regional County Municipality : in the unorganized territory of Lac-Croche; La Tuque : Lac-Saint-Jean-Est Regional County Municipality : in the unorganized territory of Lac-Moncouche; Le Domaine-du-Roy Regional County Municipality : in the municipality of Saint-André-du-Lac-Saint-Jean.