University of Canberra Associate Professor Mark Lintermans stood down from his role as chair of the NSW Fisheries Scientific Committee on Thursday in response to the state government's fast-tracking of the approval process due to the COVID-19 economic downturn.

"I cannot continue to serve a government that so willfully ignores the destructive impacts of Snowy 2.0 on two threatened fish species," Dr Lintermans, who has 30 years experience in the research and management of threatened freshwater fish, said.

The committee is an independent body working alongside government, consisting of seven experienced scientists in the fields of fish biology, aquatic invertebrates and marine vegetation; population dynamics, aquatic ecology and genetics.

Planning and Public Spaces Minister Rob Stokes said the project's approval was made with the proviso owner, Snowy Hydro Ltd, would invest almost $100 million for biodiversity and environmental offsets inside Kosciuszko National Park.

"In March we approved the Snowy 2.0 Segment Factory and this month we have approved the Snowy 2.0 Main Works, enabling the creation of new jobs and the flow of substantial investment into our state," Mr Stokes said.

Dr Lintermans said the government's granting of an exemption from "two critical provisions of the NSW Biosecurity Act" is "unprecedented", and could lead to the extinction in the wild of the stocky galaxis fish.

"The transfer of the invasive species climbing galaxias and redfin perch will have significant impacts on the critically endangered stocky galaxias and the endangered Macquarie perch," he said.

Dr Lintermans has also previously warned the government the national park's horse population is also a threat to the survival of the fish species.

He said the scheme proposes the construction of a 27km tunnel to pump water from Talbingo Reservoir on the Tumut River to Tantangara reservoir on the upper Murrumbidgee, a move that will likely transfer invasive fish species between reserviors.

Parts of the NSW Biosecurity Act are designed to prevent the transfer of invasive species, he said.

"Stocky galaxias are confined to a single 3km section of a small stream in Kosciuszko National Park, upstream of a waterfall that excludes trout," Dr Lintermans said.

"Unfortunately, the waterfall will not prevent the climbing galaxias from invading the stocky galaxias population, with climbing galaxias expected to prey upon and compete with its critically endangered colleague," he said.

"Instead of adopting the universally accepted best-practice of preventing the transfer of invasive fish, Snowy Hydro are proposing second-rate alternatives to try and contain the invasive fish after transfer."

Along with a large number of experts from a range of fields, Dr Lintermans has called for an independent review of the threats, mitigation measures, and long-term impacts of the project.

Critics of the project have also called it too expensive, inefficient, and a pollution risk.

The government said the project would create up to 2000 new jobs and $4.6 billion of investment into the region.

"Snowy Hydro is an icon of our community, with Snowy 2.0 already employing about 500 people, directly injecting more than $35 million into the Snowy Mountains and involving more than 100 local businesses," Deputy Premier John Barilaro said.

Critic of the project and former EnergyAustralia managing director Ted Woodley said the transfer of the fish species "is an intractable disaster, with no mitigating measures possible".

"It is reason enough to reject the project, let alone the many other environmental impacts, none of which have ever been approved within a national park before," he said.

"2000 construction jobs may be generated, but when construction is complete there will only be a handful of additional operational positions and a legacy of destruction across Kosciuszko and beyond.

"There are many cheaper, more efficient energy storage alternatives with far less environmental consequences."

Snowy Hydro said the first power generated from Snowy 2.0 is expected in early 2025, followed by progressive commissioning of six generating units.

"Snowy 2.0 will provide an additional 2,000 megawatts of dispatchable, on-demand generating capacity and approximately 350,000 megawatt hours of large-scale storage to the National Electricity Market," their website says.

"To provide context, this is enough energy storage to power three million homes over the course of a week."