Feral horses are running riot across the Australian Alps, with numbers exploding in the past five years prompting experts to warn of an ecological disaster.
The latest five-yearly survey of feral horse numbers shows an alarming rise in brumby populations in some of Australia's most famous natural settings.
Conservative estimates based on the research put the figure at more than 20,000 in Kosciuszko National Park and upwards of 25,000 across the alps.
Invasive Species Council chief executive Andrew Cox has urged the NSW government to take drastic action to cull brumbies.
"This is a disaster. The park is being ruined by feral horses. We're seeing unprecedented damage," he told reporters in Canberra.
He's calling for humane and effective measures to slash the wild horse population.
"The damage is indisputable. The park is being wrecked. The wetlands are being wrecked. Our catchments of three major rivers are being wrecked," he said.
"We're losing threatened species that could become extinct if the out of control horse numbers are allowed to continue."
NSW's so-called "brumby bill" has been criticised as a roadblock to controlling numbers, with the laws prohibiting lethal culling.
Mr Cox said there was flexibility to control populations under the current regime.
Australian National University professor Jamie Pittock said the horses were trampling the last remaining habitat of engendered frogs and mammals, while leaving little feed for kangaroos, wallabies and wombats.
"The hard hooves of over 25,000 feral horses are destroying the headwaters of the iconic Snowy, Murray and Murrumbidgee rivers," he said.
Mr Cox said brumbies could also threaten human life, with the horses behind a series of near-misses on roads around the national park.
"It's a matter of time before there's a fatal accident," he said.
Tom Bagnat, a former regional director at NSW National Parks and Wildlife Service, oversaw a now abandoned 2016 draft horse plan.
"We are facing a terrible catastrophe just at this moment," he said.
"Kosciuszko is one of the last strongholds of wildlife that we have left in New South Wales. If we're going to give that up to horses, what are we doing for future generations, what are we doing for wildlife?"
Mr Bagnat said there was no "silver bullet" for controlling horses, with a range of measures needed to curb the population explosion.
The ACT government has warned Canberra's drinking water quality could be at risk, with environment minister Mick Gentleman raising the issue with state and federal colleagues.
Australian Associated Press