Lac de Sylans

Lake Sylans

A listed site since 1909 and now a paradise for pike fishers, on its shores lie the ruins of old ice factories, which used to sell the ice extracted from the lake until 1917.

Formation of the lake

Lake Sylans is located in a natural cross valley, hollowed out by a river perpendicular to the mountain. Nestling at the bottom of the Nantua cross valley, Lake Sylans is an "accidental" lake. It is thought to have formed in the Middle Ages, following the collapse of a portion of the north cliff face of the Nantua cross valley (glacial moraines), which filled in part of the valley by blocking the flow of the sources of the Doye. It is supplied with water by the Charix stream. The lake water infiltrates underground through the fallen rocks and supplies the source of the Doye. In times of high water, it overflows into the Comet stream to the north-west.
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The origins of Lake Sylans

The mingling of geological layers makes it hard to date the rock slide that created the lake. Lake Sylans was long thought to have formed in the early 17th century. This assertion is now disputed since historic sources provide evidence of it existing as far back as the 12th century. Thus, a papal bull by Pope Eugene III confirms the privileges of Nantua Abbey over the “lacum Silani” in 1145.

Very pure water due to low mineral content

Filtered through the large rocks and accumulated sand, the water from the surrounding massifs that surface in the Les Neyrolles marsh is of high quality. The inhabitants of Les Neyrolles drink this naturally filtered water from the tap and the Cristaline bottling plant has been using this source of the Doye since 1977.

  • Visites estivales nocturnes - Sylans - 2014 - Mélanie Chanel (2) - Copie
  • Surface area: 49.7 ha
  • Volume: 4,800,000 m²
  • Length: 2 km
  • Width: 250 m
  • Altitude: 584 m
  • Maximum depth: 22 m


The lake’s water overflows towards Les Neyrolles, infiltrating through the rock slide to come out again at the source of the Doye. In dry periods, the water level can be much lower, whereas in wet periods, the underground passage through which the lake water is evacuated is no longer adequate. The level then rises until the lake overflows on the other side, towards Saint-Germain-de-Joux, via the Combet stream.

Lake Sylans and its people

Due to a harsh climate and lack of sunlight, the shores of Lake Sylans have never been home to people for long periods, except during the time when it was being used for ice production. Yesterday and today, the only activity on the lake is fishing.

  • Visite nocturne des Glacières
    Visite nocturne des Glacières
  • Visites estivales nocturnes - Sylans - 2014 - Mélanie Chanel (17)

The Glacières de Sylans ice harvesting factory

On the west side, the ruines of the old ice factory can still be seen. The factory marketed ice extracted from the lake (up to 40 cm thick) until 1917.

A harsh mountain climate and lack of sunlight in winter made it possible to create one of the country’s biggest natural ice factories. In 1864, Joachim Moinat, the owner of the Café du Paradis in Nantua, had the idea to use ice from Lake Sylans to cool his customers’ drinks. The ice was extracted artisanally until the business was sold to the Glacières de Paris in 1885; stone buildings replaced the wooden ones. The company then enjoyed a golden age until 1914 thanks to railway transport, which meant ice could be exported to Lyon, Paris, Marseille and even Algiers! In 1924, the land and buildings were returned to the municipalities when the lease ran out.

Fish in the lake

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Lake Sylans is a listed natural site. Its water is very pure due to its low mineral content, which explains the quality of the ice produced at this location. Very clear, even crystalline depending on the season, its water sometimes appears green. A second category lake, Lake Sylans is highly prized by fishermen due to its abundant pike, whitefish, carp and bream. It is renowned for its enormous pike. Fishing is governed by conditions set out in an annual prefectural order.

At this 2nd category lake in the public domain, if you don’t have a fishing permit, the nearest place to buy one is the Relais des Mousquetaires in Les Neyrolles (tel 04 74 75 15 29).

Top tip

You can fish for carp at night in the locality of “la glacière”


Office de Tourisme Haut-Bugey
Espace Trois Lacs 14 rue du docteur Mercier – 01130 NANTUA
Tél. +33 (0)4 74 12 11 57

On video

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