The Gagné river flows through the municipalities of Thetford Mines and Kinnear's Mills, in Les Appalaches Regional County Municipality, in the administrative region of Chaudière-Appalaches, in Quebec, in Canada.

From its source, the Gagné River flows on 6.5 kilometres (4.0 mi) towards the northwest until its confluence.

[1] The Gagné river flows at the confluence of the Osgood River with the Prévost brook in the municipality of Kinnear's Mills, in the heart of the hamlet of Plage-Lemieux.

[2] Its confluence is located 0.8 kilometres (0.50 mi) upstream of the municipal border between Kinnear's Mills and Thetford Mines.

The toponym "rivière Gagné" was made official on October 6, 1983, at the Commission de toponymie du Québec.