Lac Saint-Jean is a large, relatively shallow lake in south-central Quebec, Canada, in the Laurentian Highlands. It is situated 206 km north of the Saint Lawrence River, into which it drains via the Saguenay River. It covers an area of 1,053 km², and is 63.1 m at its deepest point. Its name in the Innu language is Piekuakamu.