After dismantling two dams, the Sélune river in Normandy has seen a remarkable ecological recovery, with salmon returning and water quality improving dramatically.
Dams removed from Sélune River
The Sélune River in the Manche region of France had its two major dams, Vezins and La Roche-qui-Boit, dismantled in 2020 and 2023, respectively, restoring 90 kilometers of river to its natural flow. This action has allowed species to move freely again and has led to unexpected ecological improvements.Ecological recovery observed
Since the removal of the dams, juvenile salmon have been spotted in the river, indicating that adult salmon have successfully swum upstream to spawn. Water quality has also improved, with the disappearance of toxic algae and the return of mayflies, which are sensitive to pollution and serve as biological indicators of a healthy ecosystem.Impact of the dams
The Vezins and La Roche-qui-Boit dams, built in 1932 and 1921, respectively, created artificial reservoirs that transformed the river into stagnant water bodies. These reservoirs disrupted the natural flow and introduced non-native species, altering the river's ecosystem and blocking the migration of salmon for nearly 90 years.History of dam removal efforts
The idea of removing the dams originated during the Grenelle environment summit in 2007, following the end of the dam's exploitation concession. However, the process faced delays and was temporarily halted in 2014 before being resumed in 2017. Removing the dams required managing the ecological impact, including the removal of 17 tons of non-native fish from the reservoirs.Scientific confirmation of recovery
Researcher Frédéric Marchand from INRAE confirmed the return of juvenile salmon, indicating that adult salmon have successfully migrated upstream to spawn. The river's water quality has also improved significantly, with the disappearance of toxic algae and the return of mayflies, signaling a restoration of the river's ecological balance.Speed of ecological renewal
The recovery of the Sélune River has been faster than expected, with signs of ecological renewal appearing within a few years of dam removal. The river is regaining its natural features, including alternating current and calm zones, suitable gravel for reproduction, and improved water oxygenation.Broader implications for river management
The Sélune case highlights the potential for ecological recovery when dams are removed, prompting a broader discussion about the management of aging hydraulic infrastructure in France. This example shows that rivers can regain their vitality in a relatively short time, offering a practical model for other regions considering similar actions.
