The Monsan River is a tributary of Lake Monsan which is crossed by the Maicasagi River located at Eeyou Istchee Baie-James (municipality), in the administrative region of Nord-du-Québec, in the Canadian province of Quebec, in Canada.

The hydrographic slope of the Monsan River is served by a secondary road along the north shore of the Waswanipi River and separating from road 113 connecting Lebel-sur-Quévillon to Chibougamau and passing in Waswanipi.

The surface of the Monsan River is usually frozen from early November to mid-May, however, safe ice movement is generally from mid-November to mid-April.

The main hydrographic slopes near the Monsan River are: The Monsan River rises at the mouth of a small unidentified lake (length: 0.4 kilometres (0.25 mi) altitude: 371 metres (1,217 ft)).

From there, it flows Southeast, Southwest, and West to the East shore of Maicasagi Lake.