Officials have voiced their concern over wildlife and the environment after a fire was deliberately started at dunes.
Denbighshire council officials say an area at Horton's Nose at the Foryd Harbour in Rhyl was set alight on Thursday.
The dunes are a haven for wildlife and regarded as a vital coastal defence.
Although actually in Conwy county, the site is owned and managed by neighbouring Denighshire council.
Coastal officers are trying to assess which animals may have been harmed.
Toni Proffitt, Denbighshire's coastal access officer, said: "It is a great shame that people have to harm such a lovely place, spoiling the enjoyment of the site for others.
"I really hope that no wildlife was affected by the fire."
The dunes are home to many species of plants and animals, including the common lizard, skylarks and burnet moths, and cormorants, sandwich terns and oystercatchers are often seen.
Officials said the "deep root network" of the marram grass stabilised the dunes and enabled them to act as a natural sea defence.