Photos taken by Kurri Landcare member Col Maybury show large chunks missing from the century-old dam spillway.

Landcare group members say the structure has visibly deteriorated during the past month.

‘‘If it collapses it will dump about 150 Olympic-sized swimming pools of water on Weston,’’ Mr Maybury said. 

The 19-megalitre reservoir was built at the turn of last century to provide water for the steam-powered Hebburn Colliery.

It has also served as a storage for acid-laced water that is pumped from surrounding abandoned mine workings.

Mr Maybury had hoped to address this week’s Cessnock council meeting with his concerns, but he was refused on the basis that the subject of flooding was not listed on the agenda.

He has also raised his concerns with local police. 

A Cessnock council spokeswoman said the dam’s condition was under investigation.

‘‘We are currently investigating this matter as it’s believed the dam in question is on private property,’’ she said.

Mr Maybury has also raised concerns about the state of the Chinaman’s Hollow bridge on Cessnock Road, which was damaged in the recent storm.

A  Roads and Maritime Services spokesman said the department had been working with the  council to assess damage to the bridge.

‘‘Council completed urgent repairs to stabilise the embankment with rocks, repair the guard rail and carry out concrete repairs to allow the road to reopen,’’ he said.

‘‘Roads and Maritime will continue inspections across the state’s road network damaged during recent extreme weather.’’