The Gamache River (French: Rivière Gamache) is a tributary of the Gulf of Saint Lawrence, flowing in the municipality of L'Île-d'Anticosti, Minganie Regional County Municipality, in the administrative region of Côte-Nord, Quebec, Canada.

The Gamache River draws its source from Lac Claude (length: 2.0 km (1.2 mi); altitude: 68 m (223 ft)) located in the western part of Anticosti Island.

From the mouth of Claude Lake, the course of the Gamache River descends on 9.4 km (5.8 mi) towards the south with a drop of 67 m (220 ft), according to the following segments: The Gamache River flows into the heart of the village of Port-Menier, on the north side of the wharf, at the end of Gamache Bay (length: 5.7 km (3.5 mi); width: 4.2 km (2.6 mi) at the entrance to the bay), on the south shore of Anticosti Island, in the Gulf of St. Lawrence.

This confluence is located at 13.2 km (8.2 mi) east of the Pointe aux Pointe-Ouest point of Anticosti Island, at 11.5 km (7.1 mi) to the southeast of the shore north of the island.

Gamache was reputed to be intelligent, skillful, gifted, daring, formidable and feared.