It’s one of our idyllic islands: a sandbank in the heart of the Arcachon Basin, the famous Banc d’Arguin, is disappearing. It has shrunk from seven to three kilometers in just 10 years. The cause: storms and beach erosion. Let’s take a closer look at this phenomenon.
Opposite the Dune du Pilat, the Banc d’Arguin(New window)It’s a small island of golden sand. Its turquoise water is the clearest in the Arcachon Basin. « It’s quite impressive. It feels like an island. You really wonder what it’s doing here! » exclaims a swimmer. Between this little paradise island and the dune, the waters are calm, because the Banc d’Arguin sandbar protects the coast from the ocean waves. But in some places, the sandbar has disappeared: « There, the Banc d’Arguin used to be here, » points out Audrey Ducros, captain of « Balade Bateau Arcachon, » who is experiencing unusual jolts with her boat. « Usually, we’re protected. When I turned around, I could clearly see that it had disappeared , » she explains.
Because now, the Arguin sandbank is submerged when the swell is strong. It’s shrinking rapidly. Satellite images at low tide show it has gone from seven kilometers long in 2016 to just three in 2026. The phenomenon is accelerating. A photograph of the sandbank in 2023, just before devastating storms, and another taken today, show the extent of the damage.
Even for the warden of the protected nature reserve, the landscape is unrecognizable. « I’ve arrived at the southern tip of the Banc d’Arguin. And you can clearly see that this whole area where the water is shallow was the Banc d’Arguin of yesterday. It used to extend all the way to the point, to the pine forest over there. And now, it’s an area completely exposed to the ocean. All of this is also partly linked to climate change. We should take advantage of the Banc d’Arguin today because I’m not sure it will still be here tomorrow, » laments Benoît Dumeau, warden of the Banc d’Arguin nature reserve.
Oyster farms and endangered birds
Already threatened with extinction, the oyster beds of the Banc d’Arguin are suffering from this erosion. Those at the southern tip were destroyed by the storms of winter 2023. Rebuilding them is impossible. David has lost three-quarters of his business: « At high tide, the waves come right over, so the area is starting to become dangerous , » he points out. « I’m mainly going to retire and stop. I’m a bit fed up , » he confides.
Erosion also threatens seabirds. In a protected area, they can nest undisturbed. The Banc d’Arguin is the only sanctuary in the region. But there are far fewer nests than before. « Where we are now, just two years ago, we were on a vegetated dune, and the gulls nested in these bushes. Erosion eventually removed this dune. The sea washed over it, destroying the eggs and the nests , » explains Adrien de Montaudoin, ornithologist at the Banc d’Arguin Nature Reserve.
The Banc d’Arguin may one day disappear completely, but the enormous quantities of sand moved by the swell could also create another islet at the entrance to the Arcachon basin.
source : france info
