The project aims to restore the ecological connectivity and hydromorphological function of the Lignon River.
The project is located on the upper Lignon, in Haute-Loire, within the Loire river basin. It concerns a section of the upper reaches situated within the “Haut Lignon” Natura 2000 site, which has been designated for the quality of its aquatic habitats and the presence of species of significant conservation importance. Among these, the freshwater pearl mussel (Margaritifera margaritifera) is the main conservation priority in the area. The brown trout (Salmo trutta), which is also present, is a host species essential to its life cycle. The Upper Lignon and its tributaries perform important functions for the reproduction, refuge and movement of aquatic species, making this sector of particular concern for an ecological continuity restoration project.
| Project status | Live |
|---|---|
| Project type | Dam removal: demolition |
| Country | France |
| River | Lignon |
| Removal timeline | July 2026 |
| Km to be opened | 1.6 km |
| Focal species | Freshwater pearl mussels (Margaritifera margaritifera) and Brown trout (Salmo trutta) |
| Organisation | SISMAE and European Rivers Network |
| Website | SISMAE & European Rivers Network |
In recent years, several projects have been carried out in the Lignon catchment area to improve fish migration and gradually restore the continuity of the river network. In this context, the Eyres weir remains a barrier on the upper Lignon. Although it is now obsolete, it continues to disrupt biological exchange and the natural functioning of the river in the section concerned.
This issue is all the more pressing as the area is home to the freshwater pearl mussel (Margaritifera margaritifera), whose life cycle depends directly on the free movement of brown trout (Salmo trutta). The removal of this structure is therefore part of a coherent approach across the catchment area, with the aim of restoring the functioning of this major river in the region and reinforcing the actions already underway on the Lignon.
The project aims to restore more natural conditions to this section of the Lignon following the removal of the structure. The expected results relate to the morphological evolution of the site, with changes in flow conditions, sediment transport and habitat organisation on the reopened section.
Two freshwater pearl mussel stations are located directly upstream and downstream of the structure, making this area of particular interest for post-works monitoring. The aim is to document the environment’s response following reopening, through monitoring the morphological evolution of the section, surveying freshwater pearl mussels (Margaritifera margaritifera) and observing the recolonisation of the upstream sector by brown trout (Salmo trutta).
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