The NSW government has been ordered to revisit world heritage assessments for the Warragamba Dam expansion.

A federal analysis has found the NSW government did not properly consider the impact of the dam expansion on several species, including the platypus.

A report by federal environment bureaucrats has reportedly been leaked to reporters at The Guardian.

It allegedly found WaterNSW did not adequately assess how the plan to raise the dam wall by 17 metres would affect world heritage values of the Blue Mountains.

Reports say WaterNSW brought in the consultancy SMEC to conduct wildlife and heritage surveys.

Questions remained about how flooding or changes in hydrology would affect the platypus and echidna, or how the sight of dead trees and shrubs would impact views from lookout points.

“The proposal has not been adequately assessed for the impacts on the World Heritage Area’s national and world heritage values and outstanding universal values,” officials wrote, according to The Guardian.

It adds to previous questions about how the government agency assessed potential impacts on threatened wildlife and Indigenous heritage.

WaterNSW says the surveys were conducted in line with planning rules and environmental assessment requirements for state-significant infrastructure projects.

The agency says that any additional studies and information that may be sought by agencies beyond those requirements will be incorporated in future version of the EIS, if necessary.