Letting thousands of brumbies roam wild through the Snowy Mountains and abandoning plans for controlled culling is "madness" and "disaster" for the nation's natural heritage, says a leading professor.
Deputy NSW Premier John Barilaro has backflipped on the state government's proposed culling plan in Kosciuszko National Park, citing the cultural significance of the brumby.
"Wild brumbies have been roaming the Australian Alps for almost 200 years and are part of the cultural fabric and folklore of the high country," he said in a statement on Sunday.
Leading scientists from around Australia have long supported plans to cull the brumby population from 6000 to 600 over 20 years, arguing it's needed to protect the delicate Alpine environment.
Professor Don Driscoll, from Deakin University, says Sunday's decision will affect natural species, natural fauna and water supply, which could also affect the Snowy 2.0 scheme.
"It's a disaster to our national heritage," he said.
"(It's) a slap in the face for wild horses, it's a slap in the face to the people who care about Australia's natural heritage and a slap in the face for the state's threatened species."
Prof Driscoll warned it could even do the horses more harm than good.
"It's also cruel to thousands of horses because of the escalating population that will starve to death due to the decline in food resources," he told AAP.
"Kosciuszko national park not only contains the nation's highest mountain but rare animal and fauna species that evolved in the region over tens of thousands of years."
For Mr Barilaro to sacrifice those things for feral horses introduced in 1820 is "madness", he added.
Prof Driscoll is part of a group of 41 scientists from 16 universities who wrote to former NSW Premier Mike Baird in 2016 saying the only way to save the unique ecosystem was to cull 90 per cent of the brumby population.
Brumbies in Kosciuszko have degraded 48 per cent of the national park.
The brumby population increased from 4200 in 2009 to 6000, despite 450 being removed each year, Prof Driscroll said.
But Mr Barilaro said that if the brumby population climbed too high in highly-sensitive alpine areas then resources would be allocated towards their relocation and re-homing.
"Kosciuszko National Park exists to protect the unique environment of the Snowy Mountains, and that unique environment includes wild brumbies," he said.