County Durham flood prevention scheme dam is subsiding
Land around an award-winning dam has started sinking after being built above disused mineshafts.
The £3m earth dam on the River Gaunless in County Durham was part of an £8.8m flood prevention scheme.
The Environment Agency said it would still work but it is spending £1.25m securing the mine workings below it.
Project manager Jonny Lyttle said of the sites available when it was building the dam, the agency had chosen the one with the fewest mine workings.
The work to secure the dam after recent subsidence was "vital" he said.
"It's something we don't take any chances with," he said.
The Spring Gardens dam was built after West Auckland and South Church were badly affected by floods in 2000.
It won the Green Apple Award for design and good environmental practice during construction.