There are no plans to re-assess the thousands of hectares of land likely to be flooded by the raising of NSW's Warragamba Dam wall despite much of the area being destroyed by bushfires.
Under the NSW government's plan to raise Warragamba Dam wall, up to 1000 hectares of world heritage area and 3700 of surrounding national park will be inundated for up to two weeks.
A NSW upper house inquiry into the wall raising on Tuesday examined the impact the summer's bushfires had on the assessment process after much of the area was burnt by the Green Wattle Creek blaze, the Grose Valley fire and the Gospers Mountain blaze over summer.
Environmentalists have raised concerns the fires could have had devastating impacts on wildlife and dozens of threatened species in the area.
National Parks and Wildlife Service deputy secretary Atticus Fleming told the inquiry preliminary modeling suggests up to 80 per cent of the potential area to be inundated by the wall raising was burnt in the fires.
"That represents a significant impact on the biodiversity of the area," he told the hearing in Sydney.
Mr Fleming added that it will take years for some areas to recover after the bushfires with concerns some may never fully recover.
Water NSW, which is preparing the environmental impact statement for the wall raising, told the inquiry that there are no plans to conduct further assessments of the area after the bushfires.
"Fortuitously, for the EIS, all that survey work was actually done well before fires," Water NSW major projects program director David Harper said.
"The guidelines don't stipulate we have to do anymore if you had already undertaken the survey prior to the bushfires."
When asked by inquiry chair Independent MP Justin Field if any further assessment or surveys were planned, Mr Harper said: "not at this stage".
The Department of Planning, Industry and Environment could advise Water NSW that further assessments need to be done to the area before the environmental impact statement is released to the public later this year.
The World Heritage Committee, which selects sites for UNESCO's world heritage list, expressed concerns over the project and will review the statement before the federal government makes the final decision.
Environmental group Give a Dam warned that by not re-assessing the area after the fires, the NSW government agencies have set the Commonwealth on a "collision course" with UNESCO in the coming months.
The Berejiklian government wants to raise the wall at least 14 metres to help prevent the risk of flooding in the Hawkesbury-Nepean Valley. The plan would allow additional floodwater to be captured and temporarily held back in the national park before a controlled release.