Marais des Bidonnes, ENS de l'Ain
Walk from the Pont des îles along a path with a few educational panels for children. Duration 1h30, flat terrain, risk of mud, in summer, risk of mosquitoes. The Bidonnes marsh straddles the communes of Divonne-les-Bains and Bogis-Bossey in Switzerland. Altitude: 470m. It is one of the last great low marshes at the foot of the Jura mountains. Access is via an educational trail that runs from the Pont des îles along the Canal de Cran. Four plant formations predominate:
- a wooded belt formed by an alder-type wet forest - a choin meadow - a mullein meadow (Molina arundinacea and M. caerulea) - compact areas of mariscus (Cladium mariscus).
Covering an area of 66 hectares, the marsh is home to some exceptional tree and animal species. 160 plants have been inventoried. Rare butterflies: 3 species of Azure, characteristic of wetlands. A number of educational panels have been installed along the path leading to the marsh. The Bidonnes marsh is managed by CREN (Conservatoire Rhône-Alpes des Espaces Naturels). Since part of the Divonne marshland was drained by the creation of an artificial body of water (Lake Divonne), the Bidonnes marsh is one of the last French marshes in the area surrounding Geneva and the Lake Geneva conurbations. It is important to preserve it as it regulates the course of the Divonne-Versoix river.
The Marais des Bidonnes was awarded the "ENS" label by the Département de l'Ain in 2015, along with the other marshes linked to the Versoix, Marais des Broues and Marais de Prodon. Real natural and landscaped jewels of the Ain department, the sites benefiting from the ENS "Espaces naturels sensibles" label are managed in such a way as to preserve the biodiversity they host and developed for opening to the public (barring exceptions due to the fragility of the environments).
