From the edge of the Haute-Savoie region in the Val d'Abondance and the Vallée des Mines d'Or, the Dranses d'Abondance and Morzine merge near the village of Bioge to form the Dranse. It then meanders between road and forest before reaching Thonon. The Dranse is one of the lake's major tributaries. Its waters are typical of a pre-alpine river, with its torrent-like high flow in spring and cold temperatures, making it an indispensable ally in the health of Lake Geneva.
When it reaches Thonon, it melts into the lake, forming a delta. One of four sites of major importance identified by the International Commission for the Protection of the Waters of Lake Geneva (CIPEL), it comprises several types of natural environment, including two main ones: dry (pebble moors) and wet (marshy areas and ponds). Since 1980, it has been a protected nature reserve managed by the Conservatoire d'Espaces Naturels de Haute-Savoie.
The Dranse delta reserve is a jewel of biodiversity: it provides a prime habitat for a large number of species, including the Common Tern, the Sleepy Poppy, the Beaver and the Lake Trout.
An observation trail has been laid out around the reserve to allow visitors to admire this beautiful wild setting. Activities and guided tours are organised by the Maison des Dranses to raise public awareness of this little paradise of unspoilt nature, whose fragile dynamics could be threatened by the surrounding industries (gravel pits, wastewater treatment plants, etc.).
