It will continue the warnings through Friday morning until it conducts an aerialsurvey to determine its sinking left behind no potentially hazardous debris, Mosley said.
No one - including Pembrokeshire National Park - realised the community existed until it was spotted by a plane doing an aerialsurvey about four years ago.
"That shows a comfort in their own security and power, in that they're happy for something as important as a water resource to be placed north of the frontier, " Dave Macleod, from English Heritage aerialsurvey team, said.