Lac d'Issarlès

Lac d'Issarlès is a volcanic lake in the Ardèche department, sitting at 1,000 metres above sea level in the commune of Le Lac-d'Issarlès, within the Auvergne-Rhône-Alpes region. Covering roughly 0.9 km², it ranks among the deepest volcanic lakes in France.

How did the lake form?

The lake fills a maar crater, produced by violent phreatomagmatic eruptions — explosions triggered when rising magma met underground water, setting off a series of steam-driven blasts. The eruptions took place tens of thousands of years ago, during a period when Neanderthals still inhabited the surrounding area; the ash and steam columns would have been visible from far off. The crater is considered one of the deepest of its kind in France, with the lake bed lying more than 100 metres below the surface.

What has the lake been used for?

In the 19th century, engineer Louis Eugène Mouline proposed piping water from Issarlès to the city of Lyon through a roughly 150 km aqueduct; the scheme was never built. Since 1954, the lake's water has instead fed the Montpezat hydroelectric plant, part of a cascade system that channels water from this volcanic plateau down toward the Rhône valley. The lake itself has been protected as a natural heritage site since 1935.

What can visitors do at the lake?

In summer, swimming is the main draw: the water stays clear and cool thanks to underground springs, and supervised beaches — including the Plage de la Pommeraie — operate through July and August. A water-sports base on the shore rents out pedal boats, kayaks and canoes, and conditions are also suitable for sailing. Anglers come for trout, pike and perch in the lake's deep, clear waters. A footpath circles the entire lake, taking around an hour to walk, and the surrounding roads are popular with mountain bikers.

How to get there and where to stay?

Le Lac-d'Issarlès sits on the high plateau of Ardèche, ringed by volcanic hills known locally as "sucs," a landscape typical of this part of the Massif Central. The village itself is a small lakeside holiday base, with most accommodation clustered around the shore. It makes a convenient starting point for exploring the wider Monts d'Ardèche area, known for its extinct volcanic scenery.

Frequently asked questions

Can you swim in Lac d'Issarlès? Yes — supervised beaches operate in summer, and the water is kept clear and cool by underground springs.

Is the lake a volcanic crater? Yes, it occupies a maar crater formed by a phreatomagmatic eruption tens of thousands of years ago.

How deep is the lake? It is one of the deepest volcanic lakes in France, with a depth of more than 100 metres.

Does the lake generate electricity? Yes, since 1954 its water has supplied the Montpezat hydroelectric power plant.

What activities are available on the shore? Swimming beaches, boat and kayak rentals, fishing, and a walking trail around the entire lake.