10 platypuses to be released within months into Royal National Park after half century absence

However, that situation will change within months with the reintroduction of the iconic species into the park.

Last year it was announced 10 of the mammals - a mixture of male and female - would be released in 2022 in a project being led by University of NSW Sydney scientists in collaboration with WWF (World Wildlife Fund) Australia and National Parks and Wildlife Service (NPWS).

The platypuses will be fitted with acoustic tags, which will enable researchers to track their progress and any breeding activity for up to two years.

UNSW has confirmed the conservation project is moving ahead and the release could occur "as early as August 2022".

A statement issued on Wednesday also revealed the results of new environmental DNA (eDNA) tests of water samples.

The tests found traces of up to 250 land and water species in the Hacking River and Kangaroo Creek, but none showed signs of platypus life.

"Platypuses once inhabited the rivers of the Royal National Park, but none have been seen there in decades," says Dr Gilad Bino, who leads the project from UNSW's Centre for Ecosystem Science (CES).

"Our hope is that by reintroducing a founding population of 10 platypuses, they will establish in the area and increase," he said.

Dr Tahneal Hawke said, "Platypuses are an integral part of eastern Australia's freshwater environment and belong in the rivers of the park where they once occurred".

The statement said the recent surveys - made with support from volunteers of Friends of the Royal - also ensured ensure sites were suitable and safe for platypus reintroductions.

The team evaluated the quality of the rivers, surveyed potential food sources, and ensured that potential threats, like sedimentation, pollution, and foxes, wouldn't threaten new platypus populations.

Based on their findings, the researchers were "optimistic the Royal National Park will be able to sustain new platypus populations".

Another platypus expert said suggestions made last year that the park's platypus population was wiped out by a chemical spill on Princes Highway were "apocryphal".

"Tragically four people were killed when a truck collided with two cars on the highway early in April, 1981," said Dr Tom Grant, from the UNSW School of Biological, Earth and Environmental Sciences.

"The truck apparently rolled over and acid was spilled into Wilsons Creek near Helensburgh.

"However there appears to be little evidence this spill reached as far down the Hacking River catchment as the locations where platypuses had been reported to that time."

Dr Grant said there were very few historical records, including from the NSW Wildlife Atlas (Bionet), of platypuses in the streams in the park and it was unknown why the species had previously occurred in low numbers or why perhaps it is now absent.

"Hopefully, the new study will provide an understanding of this knowledge gap with regard to the platypus, which also now occurs in low numbers in the freshwater reaches of the Georges River," he said.