The 300 gendarmes posted at the site in Sivens in the south of France moved into the camp after the regional council accepted Environment Minister Ségolène Royal’s to scrap the original dam project, adding a call for the immediate evacuation of the protesters.
Interior Minister Bernard Cazeneuve ordered the police to act following the vote, according to Le Monde newspaper.
Some demonstrators had already moved out in the morning, on condition that the police protect them from a counter-demonstration by farmers, and negotiations with the rest were reported to be taking place on Friday afternoon.
The area has been occupied by environmental campaigners since October 2013 and one of them, Rémi Fraisse, was killed by a police stun grenade in October last year.
On Friday morning the Tarn regional council agreed to reduce the size of the reservoir that would be created by the dam, following Royal’s decision in January to block the original project in line with the recommendations of an experts’ report.
They judged the 1.5 million cubic metres of water that would have been retained out of proportion with the area’s needs.
Royal put forward two solutions – either a reservoir that would be half as big and situated 330 metres upriver or four smaller ones.
The regional council did not vote on those proposals but its chairman, Socialist Thierry Carcenac, has declared that the second option too expensive.
After the vote he said that further studies would take place to establish whether the new dam would be built “300 metres, 200 metres or 50 metres away from the present site”.
Frence's Green party, EELV, gave a chilly response to the council's decision, declaring that it does not solve the fundamental problem that caused the protest.