The Lac de Nantua (Lake of Nantua) is a glacial lake in the southern foothills of the Jura Mountains in the Haut-Bugey historical region, located between Nantua, Montréal-la-Cluse and Port in the department of Ain, France.

The original extent of the lake, once the glaciers disappeared, was about two to three times its area in 2000 with extensions in the plain in three directions (Nurieux, Saint Martin du Frêne, Montreal).

This explains its depth (42.9 m) and its configuration in the form of ice gorge east-west areas at risk of flooding towards the plain and Port area moraines.

Its scope was much larger and was marked by two arms of lakes and large marshes from work done in 1856.

The cleared zones were cleaned and sold in 1869 by the mayor of Nantua who previously owned these areas.