The Assinica River flows into the municipality of Eeyou Istchee Baie-James (municipality) in the Nord-du-Québec administrative region, in Quebec, in Canada.

The nearest forest road is located 60.6 kilometres (37.7 mi) south-east of the lake, the road skirting the northern side of Mount Opemisca; this road joins towards the south the route 113 (connecting Lebel-sur-Quévillon and Chibougamau) and the Canadian National Railway.

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

This mouth is located at: Of Cree origin, this hydronym means "river filled with stones".

The toponym 'rivière Assinica' was formalized on December 5, 1968, at the Commission de toponymie du Québec.