The rivière des Poitras is a tributary of the south bank of the Morigeau River which flows on the south-eastern bank of the rivière du Sud (Montmagny); the latter flows north-east to the south shore of the St. Lawrence River.

The Poitras river flows in the municipalities of Saint-Pierre-de-la-Rivière-du-Sud and Saint-François-de-la-Rivière-du-Sud, in the Montmagny Regional County Municipality, in the administrative region of Chaudière-Appalaches, in Quebec, in Canada.

The main neighboring watersheds of the Poitras river are: The Poitras river has its source near a country road, in the western part of the municipality of Saint-Pierre-de-la-Rivière-du-Sud, at 10.9 kilometres (6.8 mi) south of the village of Montmagny and 8.1 kilometres (5.0 mi) east of the hamlet of Morigeau.

This confluence is located at 1.7 kilometres (1.1 mi) north-east of the Martineau hamlet.

[1] The toponym Rivière des Poitras was formalized on December 5, 1968, at the Commission de toponymie du Québec.