Home to Australia's highest mountain peak, a bevy of rare plants and animals and ski resorts; it's not hard to see why more and more tourists are flocking to the Kosciuszko National Park in New South Wales.

But for every new development that's built to accommodate the visitors, a part of the park is sacrificed.

With the snow all but gone for the season and the summer tourists starting to arrive, the ABC travelled to the park to look at just how much of an impact humans are having on the unique alpine environment.

As the snow melts, work gets underway

A truck enters the Perisher Valley Ski resort in December 2016. ( ABC News: Alison Branley )

It'll be about six months before the next snow dump lures the masses to the ski resorts at Perisher in the NSW ski fields, but in summer it's also a sight to behold.

As the warmer months roll in Perisher becomes an eerie hollow; the shops are closed and its chalets are only inhabited by a few construction workers doing maintenance.

The white runs have given way to lush green flowery meadows and the snow has melted to form flowing creeks and streams.

But it's now, in the off-season, it's also possible to get a glimpse of the stark asphalt of Perisher's carpark.

At the base of the Perisher ski field in the middle of summer. ( ABC News: Alison Branley )

If ski giant Vail gets its way it could soon be the location of an 800-bed development.

Vail bought Perisher this year for $176 million from former owners Jamie Packer and Transfield.

The National Parks and Wildlife Service (NPWS) concept plans include an ice rink, sports centre, cinema, bar and swimming pool.

An artist's impression of proposed development at the Perisher ski resort. ( Supplied )

But environmentalists are gathering, rallying the troops for a possible legal challenge.

It comes as the future of Perisher hangs on two reviews; the carrying capacity review will look at whether to have an approved figure for bed numbers in the National Park.

The other is looking at whether there should be a head lease for Perisher with a commercial landlord overseeing day to day operations, similar to the nearby Thredbo resort.

There's also talk of making better use of the park as a summer destination.

And while the resorts occupy less than one per cent of Kosciuszko National Park their presence is an ongoing thorn in the side of environmentalists.

More and more visitors are heading to the national park every year. ( ABC News: Gregory Nelson )

National Parks are crown land and environmentalists ask whether a select group of chalet and hotel owners should get prime position inside a public park instead of down the road in Jindabyne.

On another level there are real and practical concerns with slicing up the park to make way for ski runs.

As for Vail, it's on an international shopping spree. It's been buying up resorts globally and Perisher will be one of the best funnels onto international slopes.

Australians now account for the highest number of foreign visitors to Vail resorts.

The future of all these measures could hang on whether the park is coping with its current visitor numbers and whether National Parks staff can effectively manage the impact of any increased traffic.

As the ABC discovered, the views on this are as diverse as the habitats in the park.

Up to our ankles in a Sphagnum Bog

Just a short drive from Perisher, we're standing in the middle of a flowery field on what appears to be lime green sponge.

It's a surreal feeling that sits somewhere between standing on slippery moss and soft fall used in playgrounds.

Emeritus Professor Geoffrey Hope from the Australian National University has the answer for us. Professor Hope has been working in the park since the 1970s.

He tells us the mush is a uniquely Australian ecosystem, with a uniquely Australian name.

It's a Sphagnum Bog. And, its endangered.

Professor Geoffrey Hope in a field of Sphagnum Bog. ( ABC News: James Thomas )

He explains that the bogs are like a peat marsh, they act as both filter and reservoir for the alpine water that trickles through the park and into the Snowy Mountain River system.

"When the sphagnum bogs are really untrampled and in good condition they'll start to make little ponds and it's important because it's the habitat for the Corroboree frog," he said.

"It builds up and breaks up the water system.

"What these bogs are really is an island, when the fire comes this is the only green spot."

The Sphagnum Bog - a uniquely Australian name, for a uniquely Australian ecosystem. ( ABC News: Alison Branley )

In 2014 National Parks and Wildlife staff dug up and moved 150 square metres of one such bog to make way for Perisher's $4 million Freedom Chairlift at Guthega.

The sods were cut using a chainsaw and transported with a front-end loader up to 100 metres away to an area of previously disturbed bog along the old Cow Pastures poma.

The chairlift can carry up to 2,400 people each hour and increased lifting capacity to some of the parks off-piste terrain.

While it's only a relatively small section of bog, Professor Hope said its relocation was unlikely to have worked.

He's been rehabilitating bogs in the park since damaging fires swept through more than a decade ago.

"But of course I am grateful that people are thinking about restoring habitat and prepared to put resources towards this," he said.

Robert Quirk from the NSW Parks and Wildlife Service said it was important to keep in mind the ski fields took up less than 1 per cent of the 600,000 hectare reserve.

"Our efforts are focused on ensuring the impacts are minimised," he said.

From one bog to another

Contaminated water from this sewage plant was being released into Perisher's alpine streams. ( ABC News: Alison Branley )

A short drive around the corner lays a small man-made water reservoir next to a picturesque creek.

It's Perisher's sewage treatment plant and it's one of the key places in the park where the number of visitors can have a real impact.

Sewage treatment plants rely on microbes to break down faeces, but those microbes need warm temperatures. The only problem is when the park is at capacity, it's also freezing cold.

The ABC has found Perisher Sewage Treatment Plant breached its Environment Protection Licence eight times during the most recent ski season and 13 times in 2015-16.

This meant higher than acceptable levels of nitrogen, ammonia, phosphorus, and solids were detected at discharge monitoring points.

In other words, contaminated water was being released into Perisher's alpine streams and ultimately the Snowy Mountain River system.

Kosciuszko National Park key facts: Size: 6,900 sq km

Size: 6,900 sq km Mount Perisher altitude: 2054 metres

Mount Perisher altitude: 2054 metres 2014 visitor numbers: 1,449,365

2014 visitor numbers: 1,449,365 Home to: mountain pygmy possums, southern corroboree frogs, and spotted tree frog

Home to: mountain pygmy possums, southern corroboree frogs, and spotted tree frog Feral animals: brumbies, feral pigs, dogs

Professor Hope said extra nutrients in the water were a death sentence for plants and animals.

"The flora and even the aquatic life here is really used to a very, very low nutritional levels because its evolved that way," he said.

Any extra development will mean more pressure on the sewage treatment plant as visitors flush, shower and launder extra megalitres.

In the Statement of Environmental Effects for the proposal to build an 800-bed development, National Parks said the current plant could cope with the extra people, but they could also upgrade if needed.

The licence breaches, suggest otherwise.

"The question is where does it stop? They can't keep packing people in here," Professor Hope said.

"The alpine of Kosciuszko is the only one we have in the whole of Australia and that's a wonderful natural experiment that needs to kept for everyone."

Mr Quirk said last year's storms put pressure on the treatment plant.

"There is no doubt it tested the system," he said.

"The only advantages of those major storms is the dilation that occurs, the amount of water moving through the system, the actual impact is very minimal."

The NSW Environment Protection Authority said in a statement it was aware the plant had breached its limits.

"Water quality monitoring, both up and downstream, found that the ambient water quality of Perisher Creek was not affected by any of the exceedances, and there was no measurable environmental impact," it said.

A rocky road to recovery

Stand at the top of Perisher Village in summer and you can get a better view by scaling one of the rocky outcrops nearby.

But underneath the feet, even the crunchy granite itself feels unfamiliar.

It's a granite tor that's unique because of the wildlife that call it home.

The endangered mountain pygmy possum scampers around the cavernous holes between the rocks.

Keith Muir from the Colong Wilderness Foundation said past management practices by the resorts had been blamed for a direct loss of habitat for the marsupials.

"Each slope grooming requires removal of trees and granite tors so people can be safe," he said.

"And this has been continuing for decades.

"The bigger the resort the more slope grooming, the more removal of habitat for endangered mountain pygmy possums, our burramys, the vegetation that they live on."

While in the park we witness a number of these tors being excavated from Perisher and moved for a rock wall nearby.

Professor Hope said there's a bigger picture to consider, with ski slopes acting as natural barriers preventing animals moving to safer ground.

"One of the problems with development is it tends to break things up into developed and not developed so that cuts across some of the purposes of the National Park but the park does have the role of recreation and access to nature for everybody," he said.



Should you come for the day or stay overnight?

The push is on for more daytrips instead of overnight stays. ( ABC News: Alison Branley )

Far from locking up the park from people, environmentalists advocate public access.

However, they say it should be about day visitors, rather than overnight guests.

"You can't have a growth economy in a National Park. You can't continue to grow resorts as if it were Noosa Heads," Mr Muir said.

"National parks are for nature. They should be permanent, public and protected."

Professor Hope said the NSW National Parks and Wildlife Service had become used to the income from ski resort high visitor turnover, something the parks service rejects.

"Because this is one of the major revenue producing parks in NSW it's supporting really a lot of other parts of the park system," he said.

But Mr Quirk said that was not the case.

"The revenue that is raised on Kosciuszko is less than what we spend on managing the park," he said.

But then there's also human impacts, countered Professor Hope.

"Every person who stays a night means other people are bringing up things, and people repairing things and there's fuel being transported around," he said.

"They need power and water and sewerage and food and beer and entertainment and they can all be provided in places like Jindabyne.

"People should be encouraged to stay on periphery on the park and come to these areas by day."

The National Parks Service said discussion of public and commercial access to parks was a bigger question for the community at large.

"We have a magnificent series of reserves in Australia," Mr Quirk said.

"The practical reality is we have a lot of businesses based there now, which [are] focused on the snow still falling and our principal responsibility is to make sure that we manage those sites for the benefit of the park and the community.

"Kosciuszko is one of the best and we do want people to get out and I understand the environmental value, because they are not going to get that in the lounge room, they are going to get out in the park."