Assinica Lake is a fresh water body on the hydrographic slope of the Assinica River and Broadback Rivers, flowing into the Municipality of Eeyou Istchee Bay- James (municipality), in the administrative region of Nord-du-Québec, in Quebec, Canada.

The surface of Opataca Lake is usually frozen from early November to mid-May, however, safe ice circulation is generally mid-November to mid-April.

With a surface area of 93 km2, lake Assinica has a complex shape, with innumerable bays, peninsulas and a hundred islands.

The old map documents indicate that prior to 1932 the term applied to a set of lakes on the same hydrographic slope.

[2] The toponym lac Assinica was formalized on December 5, 1968, at the Commission de toponymie du Québec.