Since 2024, in partnership with the French Geological Survey (BRGM), a study is characterizing the hydrosystem of the Haut-Rhône tributaries flowing from the Retord plateau and Grand Colombier. The objective is to better understand the exchanges between groundwater and surface water. A network of probes (piezometers and limnimetric probes) has been deployed, supplemented by monthly field surveys to analyze this karst system.
A widespread low flow and early dry spells mark the current situation. Trout have been observed swimming in 2 m³ pools in the middle of dry riverbeds, illustrating the severity of the situation.
The lack of rainfall in September has exacerbated these flow reductions, endangering aquatic environments and biodiversity. Consequences include less oxygenated water, increased water temperature, reduced habitats and resources for aquatic fauna, and the drying of riparian forests. Rivers such as the Vézeronce and Dorches, both certified as Rivières Sauvages (Wild Rivers), have been heavily impacted.
The water resource is under pressure in the territory. Water is a precious common good, supporting activities like hydroelectricity, material exploitation, and agriculture, while also ensuring drinking water supply. Therefore, water usage sobriety is deemed necessary.
The study, funded by the RMC Water Agency, the Departmental Council of Ain, and the CNR, was the subject of a steering committee meeting on September 22, 2026, to present the initial data. Research will continue to assess the quantity of available water and its distribution between human use and the preservation of natural environments. The Syndicat du Haut-Rhône is working to strengthen the resilience of Haut-Rhône rivers against droughts, particularly through the preservation of wetlands and the restoration of watercourses.
