The Rivière du Milieu is a tributary of Lac de la Belle Rivière, flowing the unorganized territory of Belle-Rivière, in the Lac-Saint-Jean-Est Regional County Municipality, in the administrative region of Saguenay-Lac-Saint-Jean, in the province of Quebec, in Canada.

This valley is served by some secondary forest roads, especially for forestry and recreational tourism activities.

The surface of the Middle River is usually frozen from the beginning of December to the end of March, however the safe circulation on the ice is generally made from mid-December to mid-March.

The main watersheds neighboring the Rivière du Milieu are: The Rivière du Milieu takes its source from non-Morelle lake (length: 0.6 km (0.37 mi); altitude: 444 m (1,457 ft)) in the forest zone in the Laurentides Wildlife Reserve.

This source is located at: From its source, the "rivière du Milieu" flows over 23.2 km (14.4 mi) with a drop of 98 m (322 ft) entirely in the forest zone, according to the following segments: The Middle River pours into the bottom of a bay on the east shore of Lac Saint-Jean.