University of Newcastle Associate Professor in biological sciences Michael Mahony formally identified the endangered frog yesterday, which was found on a Dungog property in January and later handed over to the No Tillegra Dam Group.

The discovery called into question the integrity of Hunter Water's environmental assessment report and was another blow to its "flawed" ecological assessment of the dam site, Greens MP John Kaye said.

Mr Kaye said a six-day fauna survey commissioned by Hunter Water in 2007 for its terrestrial and ecology report was too short and inconclusive, putting species missed during the survey at risk.

"Approving the dam on the basis of this survey would be playing Russian roulette with the future of any number of endangered species," he said.

"Some could be driven over the edge into extinction by Tillegra. The Minister for Planning is being asked to assess the impacts on one of NSW's last free-flowing rivers without a reliable ecology survey."

Hunter Water's report stated another targetted survey was completed in 2008.

Potential stuttering frog habitats were located in two small areas at Munni Bridge and Underbank, near the Williams River.

But the habitats were deemed "too small and limited to support a viable population" in the area.

Hunter Water was unavailable for comment yesterday.

No Tillegra Dam Group called on the NSW Government to halt planning work on the dam until an independent scientific analysis of endangered flora and fauna at the site was completed.

Group spokeswoman Sally Corbett said the collection of potential threatened flora and fauna should have been conducted in all four seasons.

The report noted that the entire Tillegra site was not studied.