It comes as ACT Environment Minister Mick Gentleman urged federal Environment Minister Melissa Price to intervene in the feral horse issue under federal environment laws.

The cross-government Australian Alps Program recently started an aerial survey of the feral horse population across the alps - ranging from Canberra's Brindabellas to the Victorian alps.

The program is jointly funded and operated by the ACT parks services, Parks Victoria, the NSW park service and the federal government.

Helicopter pilots are surveying three "blocks" across Australia's alps including one just on the ACT's western border.

Australian Alps liason Brett McNamara, also the ACT's parks service manager, said the survey would be finished in six to eight weeks before the results were released publicly later this year.

"We know it's also prudent land conservation management to know what the population levels are," Mr McNamara said.

Pilots taking part in the survey fly across 5000-square-kilometre blocks of land, at a set speed and height across predesignated straight lines called "transects".

The methodology was used in the last survey in 2014, when it was estimated the alps' total feral horse was 9500.

"It gives us trend, it gives us an estimation. It's not a census in terms of counting every single horse that's out there," Mr McNamara said.

Mr Gentleman wrote to Ms Price in March and asked her to "immediately intervene in this matter".

"I fear that the continued inaction from the Commonwealth Government will lead to irreversible ecological loss," he wrote.

He received no response.

The ACT is powerless to act on the issue, which may eventually affect the capital's water supply, because of NSW laws protecting horses just across the border.

Conservationists, including Mr McNamara in his role as ACT parks manager, have raised concerns about the damage feral horses are causing Australia's alpine environments.

This includes the destruction of sphagnum bogs, delicate wetland homes to the critically endangered northern corroboree frog as well as other Australian species like the broad-toothed rat.

Horses are not native to Australia and were introduced to the high country by farmers in the 1800s. "It's that unique bio region, and the recognition of that is why the Alps program has been set up," Mr McNamara said.

Last year, the NSW government gave heritage protections to feral horses in Kosciuszko National Park.

The so-called "Brumby Bill" effectively banned lethal control methods and called for a new management plan despite the government already having one in place.

In 2016, that plan recommended Kosciuszko's estimated 6000 feral horses be reduced to 600 over two decades.

Recently, NSW Deputy Premier and Nationals MP John Barilaro backtracked on promises to start an "immediate" 50 per cent non-lethal reduction of the park's horses if re-elected.

Mr Barilaro, the Brumby Bill's major proponent, said the government needed a new horse census and management plan before horses could be removed.