US President Donald Trump has been given the go-ahead to build a coastal wall at his golf resort in Doonbeg.
County Clare planners have granted permission for "costal erosion management works".
The work will consist of two new structures and a 1km wall.
An estimated 15-20 metres of dune facing the edge of the golf course has been eroded since 2002, said Trump Hotels.
Clare County Council said it had granted permission for the development of coastal erosion management works at, and adjacent to, Carrowmore Dunes, White Strand, Doughmore Bay and Trump International Golf Links and Hotel, Doonbeg.
Opponents have four weeks to appeal against the decision, said a council statement.
Tony Lowes, of Friends of the Irish Environment said the decision "must be appealed".
"Any intervention through physical barriers will impede the natural evolution of the dune system and put at risk protected species," he added.
Joe Russell, general manager of Trump Doonbeg, said: "This decision demonstrates the council's commitment to support local business and protect the economic future of the region."
He added that the hotel group would press on with "ambitious plans to protect and expand" facilities at Doonbeg.
As part of the planning conditions, Mr Trump's resort management will have to keep a close eye on the impact on beach users, the Carrowmore dune system itself, and plants and animals.
A surfers' right of way through the Doonbeg golf course must also be protected.
Mr Trump will have to pay out more than €265,000 (£235,000) to Clare County Council to cover the cost of adding or repairing roads and footpaths in the area and other public infrastructure.
The dune system is also home to the microscopic narrow-mouth whorl snail - or vertigo angustior - which has survived since the Ice Age.
Although Mr Trump has said he is not a great believer in man-made climate change, in the original application he cited global warming and rising seas as a reason for needing the wall.
Last year, controversial plans for a 4.5m-high rock wall, running 2.8km along the beach, were abandoned in favour of a revised proposal.