The Théodat Lake is a freshwater body of the territory of Eeyou Istchee Baie-James (municipality), in the administrative region of Nord-du-Québec, in the province of Quebec, in Canada.

The map of the province of Quebec (1911) by James White, accompanying the ninth report of the Geographical Survey of Canada, refers to this waterbody "L. Geikie", of unknown origin.

Even francified in the form Michagomiche, the aboriginal toponym remained a problematic choice given names of the same root used in the same region as this lake.

Theodatus evokes the life work of Gabriel Sagard, who baptized Théodat, recollet brother and missionary in Huronie in 1623 and 1624.

[2] The toponym "Lake Théodat" was officialized on December 5, 1968, by the Commission de toponymie du Québec, when it was created.