Literally a site for sore eyes – Gundungurra traditional owners say 'Kowmung' means a place to treat eye infections because of the clear waters and plentiful medicinal plants – the river is arguably Sydney's last major wild river, and one few of us will ever see.

Paradoxically, it's the very laws that keep Kowmung pristine that could also doom it.

Sydney's Special Areas were set up to preserve the city's main water catchment but those protections mean the public cannot easily visit - and begin to advocate for it.

And so, when the Berejiklian government wants to raise the Warragamba Dam wall, threatening to flood 6000 hectares of the World Heritage-listed Greater Blue Mountains Area including the lower Kowmung, few of us will appreciate what's at risk.

"It reminds me of the Franklin," says Harry Burkitt, a campaigner at the Colong Foundation for Wilderness, referring to the landmark Tasmanian protests that stopped that river's damming. "The Kowmung's just as remote, just as wild and just as threatened as the Franklin was in the 1980s."

History may not repeat itself but it does sometimes circle back.

One of Australia's first campaigns to save the wilderness involved halting plans in the 1960s by the Metropolitan Portland Cement company to turn the Colong Caves into a limestone mine, a project that would have disrupted the upper Kowmung, Burkitt says.

"It was actually from those campaigns that the first wilderness group ever established in Australia was born," he says, referring to his organisation.

Bob Carr, the former NSW premier, is also no stranger to the Kowmung and the battles to fend off lifting Warragamba Dam's height.

Back in 1995, he hiked in the Kowmung and Coxs valleys and saw off a scheme to lift the wall 23 metres compared with the government's current plans for a 14 to 17-metre raising.

"When I die, I want my ashes to be deposited there," Carr says, adding he keeps a photo of a river crossing with Milo Dunphy – a legendary conservationist who helped map the region – in his Phillip Street office.

"It's like entering another time of the planet," Carr mused, recalling some of his memory of its "haunting beauty''.

"The golden canyon with its sand bar, the grand forest rising right up the slope [and] the happy, celebratory sound of the free-flowing river," he says. "It felt and smelt as if it would have before 1788."

Carr says he served in an era when premiers such as Neville Wran and himself would join campaigners to visit wild places and be open to be convinced that they needed to be conserved.

"It's a question whether those in Macquarie Street [where Parliament sits] have the imagination to grasp what happens if this area is destroyed," he told The Sun-Herald.

So far, the government has left it to Stuart Ayres, the Minister for Western Sydney (along with Jobs, Investment, and Tourism), to make the case for what will be a billion dollar-plus project should the wall-raising ever go ahead and the cost of offsetting the environmental damage is included.

Ayres says "all interested stakeholders" will be able to provide comment once the plan's environmental impact statement is made public.

Leaks of the draft EIS have led to an embarrassing cascade of news reports detailing how one government agency after another at state and federal level have found fault with the research.

For instance, just 27 per cent of the likely flood zone – should the wall be lifted 14 metres – have been surveyed for Indigenous culture and heritage.

And even then, of the 337 sites identified, barely a handful were visited in the one day set aside by the lead author of the Indigenous culture study, insiders say.

For his part, Ayers has stressed the benefits for residents living in downstream communities that have perhaps unwisely decided to build in the notoriously flood-prone Hawkesbury-Nepean River.

"This project ensures temporary inundation occurs behind the dam wall rather than people’s living rooms, streets and businesses," Ayres says in a regular rejoinder.

"Therefore, the only time water levels behind the dam would be higher than the current maximum levels would be infrequent, when the impacts of downstream flooding from the Warragamba Catchment are being prevented or reduced," he says, adding that any inundation would be "infrequent and temporary".

The government's case, though, became harder to make on Friday, with the country's largest insurer, the Insurance Australia Group, declaring at its annual general meeting it was no longer backing the project.

"In the past we have expressed support for the raising of the wall. However, we now have additional information concerning the probable loss of significant cultural heritage sites, and important natural habitats," IAG Chair Elizabeth Bryan said.

Ian Wright, a former catchment protection officer with Sydney Water and now a science lecturer at the Western Sydney University, says Carr's visit to the Kowmung created a stir at the time because he had effectively broken the law.

Still, the project was "dead in the water" afterwards.

"It was one of the most distant and difficult spots to get to," Wright says, adding its wildness was clear to visitors who would sometimes hear dingoes howling to each other across the valley at night. Burkitt remembers one dingo outside his tent.

The Kowmung is "in the same class" as the Gross, Colo and Wollangambe rivers "but at the top" for its pristine nature, Wright says.

The threat to the region was not just to the casuarina trees and the vulnerable Camden white gums that won't survive a spell of inundation but also to the waterways if the river ceases to flow because water backs up from Lake Burragorang.

The 74 kilometre-long river drops 816 metres as it descends from near Oberon, giving it a steep gradient as it approaches its juncture with the Coxs River.

"It'll be a big soupy whirlpool where the [Kowmung joins the Coxs]," Wright says. "The velocity of the waters will drop and they will dump sediment," harming aquatic life and covering Indigenous sites in mud.

Wright is also sceptical that the government won't just let Lake Burragorang fill more often behind a higher dam wall as climate change and a rising Sydney population boost the need for a bigger reservoir.

"The temptation will be there...to make it a more permanent storage," he says.

The Gundungurra people were known for being tall, long-haired, and fearsome. "Both coastal and river peoples were evidently fearful of these highland warriors, and remained so for many years," historian Grace Karskens writes in her book, People of the River.

For emerging Gundungurra leaders, such as Taylor Clarke, preserving the Kowmung region is important "because there's a lot of Dreaming connected to it, and it's part of our songlines".

Clarke, a Macquarie University law student, says every visit she makes to the proposed future flood zone is one of urgency.

"All the time, I'm down here, I'm trying to take in as much as possible," she says on a recent trip to the Special Area near the Coxs River.

"I'm constantly thinking, 'if I don't remember this, I'm never going to hear it again in this place'," she says as a noisy friarbird swoops by.

"Suddenly, this unbroken line of culture is going to be fractured, and I'm the last link in that," Clarke says. "It's very confronting."

By Peter Hannam