The Muy River is a tributary of the east bank of the Wetetnagami River flowing into the Regional County Municipality (RCM) of Eeyou Istchee James Bay, in the administrative region of Nord-du-Québec, Quebec, Canada.
This river crosses successively (from the upstream) the townships of Prévert, Muy and Effiat.
Forestry is the main economic activity of the sector; recreational tourism activities, second.
The Muy River Valley is served by R1015 Forest Road (North-South) passing west of the Wetetnagami River Valley; this road joins the road R1051 towards the North (East-West direction). Route R1053 (East-West) intersects the lower part of the Muy River.
The surface of the Muy River is usually frozen from early November to mid-May, however, safe ice movement is generally from mid-November to mid-April.
At various times in history, this territory has been occupied by the Attikameks, the Algonquin and the Cree. The term "Muy" is a family name of French origin.
The toponym "rivière Muy" was officialized on December 5, 1968, at the Commission de toponymie du Québec, when it was created.