Lake Nemiscau (in French: Lac Nemiscau) is a freshwater lake, located in the municipality of Eeyou Istchee James Bay, in the administrative region of Nord-du-Québec, in north-western Quebec, in Canada.

The nearest village is the town of Nemaska, about 60 kilometres (37 mi) northeast.

The designation "Nimisco Lake" appears on an old card entitled "Partie de la Nouvelle-France" (Part of New France), by Alexis Jaillot, Paris, 1685.

The designation "Lake Nemisko" is on the "Map of Canada or New France and who Discoveries there have been made", by Guillaume Delisle, Paris, 1703.

The spelling" Nemisco L. appears on the card entitled "A New and Exact map of the Dominions of the King of great Britain on the continent of North America", [London], in 1715, revised in 1732 or after.