The main neighboring watersheds of the Fortier river are: The Fortier River has its source in the mountains, at 1.3 kilometres (0.81 mi) at south-west of a summit (elevation: 506 metres (1,660 ft), at 3.6 kilometres (2.2 mi) west of hamlet "Le Cent-Ans" and 4.1 kilometres (2.5 mi) south of William Lake.

From its source, the Fortier river flows over 8.8 kilometres (5.5 mi) generally North, with a drop of 237 metres (778 ft), divided into the following segments: The Fortier river empties on the south-est bank of the Bécancour River (via William Lake) at the end of a peninsula which located north of Langlois Bay.

This confluence is located 3.3 km north-west of the downtown of Saint-Ferdinand.

The term "Fortier" turns out to be a family name of French origin.

The toponym "rivière Fortier" was made official on August 17, 1978, at the Commission de toponymie du Québec.