UNESCO's World Heritage Committee has urged Australia to submit an updated environmental impact statement for a controversial proposal to raise the wall of the Warragamba Dam before any final decisions regarding the project are made.
The committee on Wednesday found the proposal was incompatible with the world heritage status of NSW's iconic Blue Mountains.
The WHC adopted a recommendation from the World Heritage Centre requesting the NSW and federal governments to submit an environmental impact statement that assesses all potential impacts on the outstanding universal value of the area, by December next year.
The decision noted concerns that raising the dam's wall by 14 metres is expected to increase the frequency and extent of inundation of the world heritage-listed site.
A UNESCO advisory body had previously warned that raising the wall could flood up to 1000 hectares of world heritage area and 3700 hectares of surrounding national park.
Former NSW environment minister Bob Debus spoke about the concerns of several conservation groups at the WHC's annual meeting in Azerbaijan, which began on June 30.
"The area proposed for inundation includes at least 300 known Gundungurra Aboriginal cultural sites, which would be damaged," he said in his speech, a copy of which was provided to AAP.
"Its cultural and conservation value is exceptional even within the Blue Mountains area."
Mr Debus said Australia's failure to protect the area would not be an "isolated misfortune" but would rather amount to "a fundamental attack" on the World Heritage Convention.
The project came under scrutiny earlier this year after AAP revealed the Berejiklian government was planning to raise each end of the wall - the dam abutments - by 17m so it could easily be modified in the future to hold back additional water.
The state government insists raising the wall will help prevent flooding of the Hawkesbury-Nepean Valley.
