The Mistassini River is a river in central Quebec, draining into the north-western portion of Lac Saint-Jean. The Mistassini River is 298 km or 185 miles long. Its source is between Eau Froide Lake and De Vau Lakes in the eastern-most portion of the vast Baie-James territory.
The upper portion of the Mistassini is characterized by a succession of rapids, waterfalls, and cascades. Only the last 15 miles, from its mouth to Dolbeau-Mistassini, is navigable.
Tributaries of the Mistassini River include the Papillon River, the Framboises River (Raspberry River), the Rats River (Rat River), and the Mistassibi River.
During the New France colony in the 17th century and first half of the 18th century, the Mistassini River was used as one of the primary access routes to Lake Mistassini. A 1679 map by Louis Jolliet shows the river with the name Kakigoua. Later the river is named Sables River (Sand River) on maps by Laure in 1731 and 1732, Jean Baptiste Bourguignon d’Anville in 1755, and Jacques-Nicolas Bellin in 1764.
Botanist Andre Michau first calls it Mistassini River during his exploration of the area in 1792. It seems that the first topographic use of this name goes back to 1825, when Pascal Tache publishes a map in which he uses the name Mistassini.
Note than despite its name, Lake Mistassini is not in the drainage basin of the Mistassini River, but is about 80 km or 50 miles west from its source. The Mistassini River is alsoconfused with its tributary, the Mistassibi River.