Marais de Lavours National Nature Reserve, National nature reserve near Culoz-Béon, France

Marais de Lavours National Nature Reserve covers 474 hectares of marshland at the foot of the Grand Colombier massif, in the Ain communes of Culoz-Béon, Ceyzérieu, Flaxieu and Pollieu. Reeds and brown stalks fill the flat wetland, low bands of mist hang over the vegetation, and a line of darker trees marks where the marsh meets the mountain. Peat at the centre of the bog is about 10 metres thick.

After the last glaciation, around 15,000 years ago, the melting Rhône glacier left a large lake that covered the whole valley, fed by the Rhône and the Séran, which carried in sediment. The lake gradually silted up, leaving only Lake Bourget in its deeper basin, and the marshes of Lavours and Chautagne took its place. Plant debris falling on the flooded ground formed peat at about one metre per millennium; the centre of the peat bog is now 10 metres thick.

Since the 12th century, livestock farming has been the marsh's main activity, alongside peat and clay extraction. In summer, hay was cut and used to mulch vines and as cattle bedding. After the rural exodus of the late 19th century, farming declined and the marsh gradually wooded over.

A 1,800-metre educational boardwalk on stilts gives access to the heart of the marsh and is open freely all year. The reserve lies at the foot of the Grand Colombier, spanning Culoz-Béon, Ceyzérieu, Flaxieu and Pollieu. The path crosses reeds and wet meadows where the mist often hangs low; keep to the boards and use the observation points to watch birds without disturbing them.

Grazing animals including Highland cattle and several horse breeds have managed the vegetation since the 1980s, creating a living landscape that develops through their natural movement and feeding. This approach keeps the ecosystem balanced while avoiding heavy machinery that might damage the delicate peat layers.