Lac au Sorcier, lake in Saint-Alexis-des-Monts, Mauricie, Canada

Lac au Sorcier is a lake of 8.7 km² in the Mastigouche wildlife reserve, in the municipality of Saint-Alexis-des-Monts, Maskinongé RCM, Mauricie, about 80 km northwest of Trois-Rivières. It lies 346 m above sea level and measures roughly 7.7 km north to south and 7.2 km east to west. Mixed forest covers its surroundings, in a thinly populated area of about 2 inhabitants per km².

The lake became part of the Mastigouche wildlife reserve in 1971 and received additional protection through the creation of the Basses-Collines-du-Lac-au-Sorcier biodiversity reserve in 2008. This protected status has helped preserve the wild surroundings and maintain water quality.

The name comes from an old Indigenous legend: a sorcerer is said to haunt the lake's island, keeping people awake with strange noises. The lake is known for salmonid fishing, mainly ouananiche and brook trout, and lies within the Mastigouche wildlife reserve.

Access is by daily fishing permit only, drawn by lottery on the sépaq.com site before 31 March; no more than 5 chaloupes may be on the water per day, with a maximum of 3 anglers per boat. The lake lies in the Mastigouche wildlife reserve, about 80 km northwest of Trois-Rivières, and covers 8.7 km².

The lake's name comes from an old Indigenous legend: a sorcerer is said to haunt its island, keeping people awake with strange noises. The story is recorded in the toponymy of Lac au Sorcier.