Dam busters: Tearing down concrete walls to save Atlantic salmon

In France’s western Normandy region, the Selune River flows into the famed Mont-Saint-Michel bay. This is where Jean-Marc Roussel and his team of scientists are carrying out a series of experiments to check the river's vital signs.

"We're like river doctors," he explains.

In 2019, a 35-metre-tall dam was removed from the Selune, while the demolition of a second dam is also underway. It’s the largest dam removal project of its kind in Europe, and a unique opportunity to investigate what happens once nature has reclaimed its territory.

The team of scientists from France’s National Institute for Agricultural Research (INRAE) capture migratory fish and insects to count them, measure them and find out how quickly ecosystems are being restored. 

The results have exceeded their expectations.

"The way the river has been reborn is such an important message, a message of hope," says Roussel. "Just when you think that everything is going wrong with the environment, sometimes you can get a sign, a concrete example of nature reclaiming its territory. And I think that’s really comforting."

Are dams really worth it? And what happens once they’re no longer in use? 

Roberto Epple has been grappling with those questions for more than a decade. As president and founder of the non-profit European Rivers Network, he is a fervent advocate of free-flowing rivers.  

He takes us to one of the many dams that have been abandoned in Europe. The Chavanon dam was built more a century ago but never completed and has been obstructing the river ever since. There could be more than 500,000 dams like this one, says Epple – obsolete and forgotten. 

At the time they were built, their end of life was never factored in. But now, energy producers are having to