The ambitious pumped hydro project recently lodged plans with NSW planning authorities for an additional four hectares of woodland to be cleared, bringing the area of Kosciuszko national parkland set to be disturbed to a total of 112 hectares.

Four hectares of woodland inside Kosciuszko National Park are set to be cleared for test drilling as part of the already approved Snowy 2.0 exploratory works.

National Parks Association of NSW chief executive Gary Dunnett said Australia's alpine environments were already under stress from climate change.

"National parks are not a place where you do large scale vegetation clearance," Mr Dunnett said.

But he said the "fractured" way the various developments required for the project were being presented hid its true environmental impact.

"The impacts of this project haven't been disclosed to us. They've crept up on us and they're only being exposed in a very piecemeal fashion," Mr Dunnett said.

Mr Dunnett said that way it would be hard tell whether the environmental impacts outweighed the project's claimed benefits.

He said the community needed a chance to comment properly on the project.

"It's almost impossible to do that when you have this drip feed approach," he said.

Snowy 2.0 - to be run by company Snowy Hydro - will create storage capacity for the massive hydro energy plant, creating tunnels from the Tantangara reservoir to the lower altitude Talbingo reservoir.

This would allow the plant to pump water downstream, creating energy during peak demand, then pump the water upstream when demand was low to replenish the Tantangara reservoir.

Because it had been declared "Critical State Significant Infrastructure", Snowy 2.0 didn't need development consent but required an environmental impact statement for approval by the NSW Planning Minister Rob Stokes and federal Environment Minister Sussan Ley.

Mr Dunnett said there had been no consideration of alternative sites for pumped hydro across the state and pointed to recent research that had identified hundreds of potential alternatives in NSW.

Chief executive Paul Broad said Snowy 2.0 would make use of existing dams, meaning there would be no change to environmental flows or new dam structures required.

"A significant advantage of Snowy 2.0 over other possible pumped hydro sites is that it is fully integrated into the existing Snowy Scheme," Mr Broad said.

He said Snowy 2.0 could not proceed without the exploratory works.

The latest modification would see almost four hectares of woodland cleared in the park to allow the drilling and road access.

Almost two hectares of that land to be cleared is habitat for the smoky mouse, a native Australian mouse, which is listed as critically endangered in NSW.

In 2009, scientists estimated less than 50 smoky mouse adults to be alive in the wild in NSW. Documents lodged with NSW planning authorities by Snowy Hydro said the clearing would account for about one per cent of habitable land for the species in the region.

Across the 112 hectares, small parcels of land for various threatened species would also be disturbed, including about 0.3 hectares of alpine tree frog habitat and almost three hectares of Booroolong frog habitat. Both frogs are listed as endangered in NSW and the Commonwealth.

Mr Dunnett said compared to how a proposed four hectares of clearing outside a city suburb was advertised, the chance for public comment on the latest modification, 30 days, was too brief.

He said "more controversial" projects had chance for comment extended.

Snowy 2.0 has recently sought approval for construction of a segment factory outside Cooma, which would see a section of habitat for the rare Cooma grassland earless dragon destroyed.

A Snowy Hydro spokeswoman said the section to be cleared was in an industrial part of the alpine town, consisting of degraded grassland.

"We are committed to avoiding, minimising or offsetting any environmental impacts of the project," the spokeswoman said.

"Our full environmental impact statement is expected to be submitted in September 2019."