The Breynat River is a tributary of the Harricana River in the municipality of Baie-James in the administrative region of Nord-du-Québec, in Quebec, in Canada.

The surface of the river is usually frozen from early November to mid-May, but safe circulation on the ice generally occurs from mid-November to the end of April.

The main hydrographic slopes adjacent to the Breynat River are: The Breynat River derives its source from a forest brook (altitude: 263 metres (863 ft)), located in the Township of Martigny in the municipality of Eeyou Istchee Baie-James (Municipality), at the Northwest of "Lac aux Épices".

The source of the Breynat River is located at: From the source, the Breynat River flows more or less in parallel to the Harricana River on 61.1 kilometres (38.0 mi) in the following segments: The Breynat River flows on the West bank of the Harricana River to: The name "rivière Breynat" was officialized on December 5, 1968, at the Commission de toponymie du Québec, meanings at the time of its founding of this commission.

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