"The concern we have is that our valley is a very precious part of the world, and they're not saying pumped hydro can't be in a national park," Leif said.

What's being promoted by the NSW government doesn't involve putting dams on rivers - it's about encouraging private development of new off-river, closed-loop pumped hydro infrastructure.

Pumped hydro is a way of storing energy that involves two reservoirs at different heights connected by large pipes.

Water is pumped to the upper reservoir using cheap wind or solar energy, and it's released later to flow through a turbine and generate electricity when demand is high.

Because of its scale and its ability to be used strategically in response to system needs, pumped hydro is a very economically efficient form of energy storage.

In December, the Department of Planning and Environment released a glossy booklet showcasing six regions in NSW with strong pumped hydro potential, based on mapping analysis carried out by the Australian National University.

Titled NSW Pumped Hydro Roadmap, it identifies 50 terawatts of off-river pumped hydro opportunities, with almost half (22.6TW) clustered in the north east of the state.

"The North East has excellent pumped hydro potential, with high opportunity scores across the region, and particularly strong opportunities in the area between Armidale and Coffs Harbour," the booklet says.

The ANU study specifically noted that their mapping exercise ruled out "areas on national parks, world heritage sites and valuable agricultural land".

"Initially we were happy to see that the roadmap was saying clearly there should be no pumped hydro in national parks and world heritage sites," Leif said.

"But when we then looked at another document, the Handbook for large-scale hydro energy projects, which is the information that goes to developers, it says that national parks possibly could be used."

A section of the Handbook, 'Securing access to land', notes that commercial investors proposing a large scale pumped hydro project would need access to land for the reservoirs and associated water pipes and transmission lines.

If such land is privately owned, they would negotiate directly with the landowner, but "more consideration is needed if any part of the land required is a national park", this document says.

This is the paragraph that worries Leif and Craig: "Proponents should obtain their own independent advice on any requirements or restrictions under the National Park and Wildlife Act 1974 if their project, or part of their project (including associated water pipes and transmission infrastructure), is to be carried out in a national park."

Leif agreed that once the infrastructure was installed, it would be a "fantastic" system with a long life, hugely cheaper and more efficient at storing energy than alternatives like batteries, but he'd prefer disused underground and open-cut mine sites used instead.

"It's not that we don't want to see pumped hydro," he said. "But these pipes would be at least a metre in diameter. There would be huge big scars coming through the national park."

Leif was one of the people responsible for having the Bellinger River National Park declared in 1996 and he's also been campaigning to see it gain world heritage status as part of the Gondwana Rainforests of Australia.

"I'm keen to see pumped hydro, but I would want them to stick to what they said about national parks and world heritage areas being excluded," he said.

Asked to comment on the concerns expressed by Leif Lemke and Craig Nelson, a spokesperson from the NSW Department of Planning and Environment supplied the following statement:

"It is important to note that neither document outlines planned development or recommends specific sites for development of large-scale hydro.

"The NSW Pumped Hydro Roadmap, developed in collaboration with the Australian National University, is a research document outlining potential development opportunities for pumped hydro throughout NSW.

"The Handbook is a guide only to the current regulatory framework that will apply to large-scale hydro energy project proposals.

"It notes legislation that applies constraints to development on some land, including national parks, Crown land or Commonwealth land."