A birdwatchers' hut has been burned down in a suspected arson attack.
A hide has been in place at Crimdon Dene for the last 14 years, giving people a shelter so they can watch the Little Terns as they visit the East Durham Coast each May from West Africa.
The hut was replaced last spring at a cost of £3,500.
It had been cleared of anything of value, but leaves the Durham Heritage Coast Partnership searching for cash to replace it.
Niall Benson, heritage coast officer, said: "We are desperately disappointed at this mindless act of vandalism.
"That's not just for the loss of the wardens' hut, but also the focal point for an important place on our coast and also for the volunteers' efforts.
"That's what we care about, those who want to come along and enjoy our coast and also the wildlife itself.
"We have austerity and now adversity, but we will replace the hut, whether it's this year or next year."
A spokesman for Durham Constabulary said: "Police are investigating a case of arson at Crimdon Dene, where the new Little Tern Hut, which was erected last year, has been burned to the ground.
"This is believed to have occurred overnight.
"Police would appreciate any information regarding this incident."
The fire broke out at the hut last night or early this morning.
Anyone with information is asked to ring 101 and quote DHM-15012018-0044.