A state Nationals MP has lodged a private member's bill to extinguish one of NSW's largest national parks, a move that opponents say signals an "open season" on the state's natural heritage.

Austin Evans, the member for Murray, is demanding the 41,000-hectare Murray Valley National Park revert to a state forest to allow timber harvesters back in.

The Murray River winds through the Murray Valley National Park - a conservation zone the local MP Austin Evans wants to revert to a state forest. Nick Moir

Mr Evans, an engineer by training, campaigned for the degazetting of the eight-year-old park during his narrow byelection win over the Shooters, Fishers and Farmers candidate a year ago.

How the Liberals-dominated Berejiklian government responds could reveal how much it is prepared to cede sway over environmental issues to its junior coalition partner to bolster support in rural areas ahead of the March state election.

A national park has not been reversed in NSW before, and such a move would likely rile environmentalists who had fought for three decades to win support for the region's conservation.

'Supportive'

"My expectation is [the government] will be supportive of it," Mr Evans told Fairfax Media.

"I think they are having discussions at the moment," he said, adding he hoped for a second recording of his bill by the year's end.

A spokesman for environment minister Gabrielle Upton declined to say which way the government was leaning.

"This is a private members bill," he said. "The NSW government will respond to it in due course."

Mr Evans said his community felt short-changed following the park's creation, saying compensation offered to buy out timber workers was "less than the timber industry earned in a single year".

Promises of a boost in tourism had also been "an absolute furphy", with visitor numbers to the region dropping, he said.

'Open season'

But Labor, the Greens and environmental scientists who helped make the case for the park, warned of an "open season" on conservation if the government bowed to Mr Evans' demands.

Is the fight over forestry versus conservation and tourism in Murray Valley National Park about to resume? Gavin Hansford/OEH

Penny Sharpe, Labor's environment spokeswoman, said the National Party had revealed "their anti-national parks" plan to roll back protection, which lately had included clearing obstacles to flooding parts of the World Heritage-listed Blue Mountains National Park by raising the Warragamba dam wall, and preserving feral horses in the Kosciuszko National Park.

“This bill might not be debated before the election but it is clear what the agenda is," Ms Sharpe said. "A re-elected Berejiklian government will abolish this and other national parks.”

Cate Faehrmann, the Greens environment spokeswoman, said Premier Gladys Berejiklian had declared an "open season on the environment to appease the dinosaurs in the National Party".

“This bill is just the tip of the iceberg," she said. "Right now the Liberals are approving massive increases to the amount of native forest that can be clear-felled [and] reducing protections from logging for koalas and other threatened species.”

Species at risk

Matthew Colloff, an ex-principal CSIRO research scientist who has written extensively on the region's ecology, said the protected area includes "some of the best river red gum forests in the central Murray region".

The region contains wetlands of international significance and various vegetation types which

are habitat to more than 60 terrestrial animal species and 40 plant species listed as threatened under state or Commonwealth legislation.

Species at risk include the superb parrot, barking owl, fishing bat and brush-tailed phascogale, a small carnivorous marsupial.

John Williams, a former commissioner, agreed more support could be given to aid tourism but rejected Mr Evans' call for degazetting the national park.

"My only modification would be to ensure we conduct well-designed ecological thinning in the national park where it is needed to enhance and preserve habitat quality and biodiversity," Dr Williams said.