It flows south for 132 kilometres (82 mi) to the Manicouagan Reservoir.

Tributaries include the Labadie, Tuk and Pipichicau rivers.

In its lower 80 kilometres (50 mi) it widens to form the western arm of the reservoir, formerly Lake Manicouagan.

However, a toponym survey conducted in 1979 reported that the Innu name used to describe the lake was Mûshaualâkan, which means "to stretch out the nets to open waters".

Pierre-Michel Laure [fr] shows R. Moucha'ouragane on his map of the Domaine en Canada (1731) and the explorer Albert Peter Low mentioned Mouchalagan River in 1895.