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Key figures

Origin and history

Lake Chalain is a 232-hectare glacial lake, the tenth largest natural lake in France, situated in a remote feature of the Jura massif, in the commune of Fontenu. Formed by a glacier of the Quaternary, it is framed by limestone cliffs of 60 to 80 meters and extends 2.7 km long and 1.1 km wide, with an average depth of 16.2 meters. Its waters, fed by karst sources, flow into the Combustion of Ain via the Egg Beef, a 2 km canal operated for hydropower.

Archaeological excavations carried out in 1904, then in the 2000s, revealed an occupied lake town from the Neolithic (-4000 to -750) at the Bronze Age, with exceptionally preserved remains: tools, weapons, wooden or leather clothing, and a monoxile canoe of 9.35 meters dated -959. These discoveries, classified as historical monuments in 1911 and registered at UNESCO in 2011, reflect an ancient human occupation, although partially destroyed by the artificial lowering of the lake in 1904.

In the Middle Ages, a hunting castle-relais was built around the 13th century on a hill of the remote, rebuilt in the 16th and 18th centuries, then abandoned after a fire in 1945. The site, acquired by the Jura department, is today a major tourist destination, although recent measures (closure of the campsite in 2022) aim to preserve its ecosystem threatened by eutrophication and trampling of protected areas.

The lake is home to a rich biodiversity, with plant species protected on its calcium banks, vulnerable to human activities. Since 2023, the level of the lake is no longer artificially lowered, ending the temporary beaches to limit the environmental impact. Water activities (sail, diving, fishing) remain popular, but motor navigation is prohibited to preserve the tranquility of the site.

Archaeological remains, including stilt houses built 5,000 years ago, rested on oak or ash poles, with walls reinforced with bryophytes. Part of this heritage was damaged by tillage, agricultural drainage and mass tourism before the current protective measures. Discovered objects, such as Chalain's canoe, are exhibited at the Jura Archaeology Museum in Lons-le-Saunier.

In 2022, a tragic accident marked the recent history of the lake: a car slipped onto an ice plate before sinking, causing the death of four occupants. This event recalled the risks associated with winter use of the site, now managed by the Régie départementale du Domaine de Chalain, which promotes sustainable and local tourism.

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