Lac de Nantua, Glacial lake in Nantua, France.

Lac de Nantua is a glacial lake in the Jura Mountains, on the commune of Nantua in the Ain. It runs west to east for 2.7 km, is 650 m wide and covers 141 hectares at an altitude of 475 m, reaching a maximum depth of 42.9 m. Its far shore is backed by a steep ridge of dark green trees and grey rock faces.

The lake was carved by glacial action during prehistoric times and kept its character for centuries. In the 1800s, water level work reshaped its dimensions to the form visitors see today.

The lake's name comes from Nantua, the town on its eastern shore. In the 19th century, the drained marshes were sold to private owners in 1869, and the lake remains a setting for walking and fishing. During World War II, resistance fighters dumped empty Allied supply containers into the water; these lie between 15 and 25 metres deep.

The lake lies at 475 m altitude, 2.7 km long and 650 m wide, with its outflow at a single point, the Bras du Lac, which joins the Oignin. The D 1084 runs along the western shore between Saint-Martin-du-Frêne and Port, where glacial moraine material is exposed in road cuttings. The 1936 classification bans new signage and requires power and telephone lines to be buried.

During the Second World War, local resistance fighters dumped empty supply containers parachuted by the Allies into the lake; the cylinders, which had held food, equipment or weapons, can still be seen at depths of 15 to 25 metres.