[1] The name Mistassibi, only in use since the late 19th century, comes from the Innu-aimun language, meaning "large river".

Its alternate name used to be Rivière aux Foins (Hay River).

It passes through Lac au Foin (Hay Lake) and among its tributaries are the aux Oiseaux, du Dépôt, and North-East Mistassibi Rivers.

[1] The company Minashtuk Inc. operates a 12 MW run-of-the-river hydroelectric power station on the Mistassibi River since 2000.

This article related to a river in Quebec, Canada is a stub.