The New South Wales government has been warned that raising the Warragamba dam would do “irreparable damage” to the Blue Mountains region.

The Government’s own advisory panel has raised concerns about the proposal to boost the wall’s height by close to 14 metres.

The greater Blue Mountains world heritage area advisory committee wrote to NSW environment minister Gabrielle Upton and federal environment minister Melissa Price in September, outlining issues with the proposal.

The letter, seen by AAP, said the project would have “significant adverse impacts” on biodiversity, wilderness and wild river values, Aboriginal cultural heritage values and aesthetic values.

“The committee urges the NSW government to very carefully consider the adverse impacts of the greater Blue Mountains heritage area when final decisions are being made about the proposed works,” committee chair Bruce Leaver said in the letter.

Raising the wall would require flooding through a “controlled release” of water, which the committee says could block beyond repair.

“The proposal to raise the Warragamba dam wall will cause irreparable damage to these extraordinary wilderness areas and wild rivers, protected under legislation,” the committee said.

The dam’s owner and operator, WaterNSW, said the details about the potential impacts on the heritage-listed area have been on the public record for over a year.

The final plan is expected to be made public in 2019.