"The whole lot potentially could drain into one river which goes through the middle of the town of Amlwch

Alan Kelly, Amlwch Industrial Heritage Trust

A council-led project group is investigating ways of avoiding a repair bill which could run into millions of pounds.

It will investigate the possibility of draining or treating the acidic water on-site.

Copper mining had taken place at Parys Mountain for centuries, until it was brought to a halt in 1915.

Since then, its distinctive landscape has proved popular as a location for science fiction films and TV programmes, including Dr Who.

Mining legacy

But over the decades, rainwater has seeped through the rocks, picking up dangerous heavy metals and forming a polluted lake.

Cracks have now been discovered in the dam holding back the water.

Alan Kelly of the Amlwch Industrial Heritage Trust said if the dam gave way, it could result in a catastrophe.

Alan Kelly says the water is very dangerous

"You've 120 foot high of water, roughly, inside there, " he said.

"The pH (level) can get down as low as 1.5, which is very acidic.

"The whole lot potentially could drain into one river which goes through the middle of the town of Amlwch."

The council's executive committee was told on Monday that a number of possible solutions were being investigated by the Mynydd Parys Project Group

They included contingency plans in event of the dam's failure, and a scheme which would see the acidic water drained and treated on site.

The site has been used for science fiction movies

Councillor Keith Thomas, who has responsibility for technical services, said: "Part of this funding will allow a specialist consultant to continue advising the project group whilst proposals are developed.

"They would then be the subject of funding applications to the Welsh Development Agency and National Assembly for Wales."

The Mynydd Parys Project Group includes the Anglesey County Council, Environment Agency, Amlwch Industrial Heritage Trust, the Anglesey Mining Company and other funding bodies.