When an ancient glacial lake in a remote and wild part of Tasmania was flooded in 1972, a movement was born.

Lake Pedder was inundated when a dam system was established in the state's south-west by the Hydro-Electric Commission, now Hydro Tasmania.

The flooding turned it from a 10-square-kilometre lake to a 242-square-kilometre reservoir.

"The heart of the south-west wilderness was lost when Lake Pedder was flooded," former Australian Greens leader Christine Milne said.

"It represented the extreme of hydro industrialisation, and the loss of Lake Pedder in many ways led people to double their efforts to save the Franklin River from hydro in the following decade."

Lake Pedder from the Frankland Range. ( Supplied: Graham Wootton )

A treasure beneath the surface

The world's first green political party evolved from the No Dams protests, which successfully stopped the damming of the Franklin River in 1983.

Ms Milne, who was arrested and spent time in jail during the protest known as the Franklin Blockade, is part of a nostalgic campaign to restore Lake Pedder with the support of another former Greens leader Bob Brown.

"It remains, underneath the impoundment, a magnificent beach, which was large enough to see light planes land on it during the summer," she said.

"It was a magnificent natural area, unique and known throughout the world as a globally significant and iconic area.

"To lose it was really gut-wrenching for people who love the Tasmanian wilderness."

The green political movement was born from the No Dams protests. ( Supplied: National Archives of Australia )

The summer of 2021–22 will be 50 years since the flooding, which saw the white quartzite beach lost beneath the surface, and the Restore Pedder campaign now wants to pull the plug and drain the lake.

If the ambitious project ever went ahead, it would be one of the world's largest ecological restorations.

But draining a lake on the scale of Pedder would not be a simple task, and convincing Hydro Tasmania and the State Government may be all but impossible.

The State Government argues that Lake Pedder is a vital part of Hydro Tasmania's renewable energy infrastructure and it is responsible for about 6 per cent of its total revenue, which is up to $30 million every year.

Conservationists campaigned against the flooding of Lake Pedder, to no avail. ( Supplied: Whatever Happened to Brenda Hean, the movie )

'Hydro went too far'

Then premier, 'Electric' Eric Reece, and the hydro commission pushed ahead with the flooding of Lake Pedder despite large protests and financial offers from prime minister Gough Whitlam.

At the time, Mr Reece said Tasmania needed to double its output of power over 10 years to meet the state's economic and social needs.

Lake Pedder's national park status was revoked and the Huon and Serpentine Rivers were dammed turning Lake Pedder into an impoundment and Tasmania's second largest lake.

Former Australian Greens leaders Bob Brown and Christine Milne. ( Supplied: Restore Pedder )

"Tasmania built a series of hydro dams and went too far in terms of wanting to dam virtually every river that they possibly could," Ms Milne said.

The dam developments led to Tasmania's energy becoming almost 100 per cent renewable and while the state has been able to import coal power through Basslink since 2005 it proudly spruiks its clean, green power.

Hydro Tasmania makes many millions selling its power interstate through Basslink, and has plans to expand its assets even further.

Its goal is for Tasmania to be self-sufficient on hydro energy, while using fluctuating energy prices to its advantage.

The Greens are often criticised for the party's past opposition to dams, in a landscape where clean renewable energy is now lauded.

"It's not a green thing to be saying something is renewable energy if it is destroying an ecosystem," Ms Milne said.

Protesters trying to stop the Franklin Dam, which did not go ahead. ( Supplied )

Why now?

Since the 1990s there have been campaigns and attempts to restore Lake Pedder to its pre-1972 level, including the Pedder 2000 campaign that wanted it drained by the turn of the millennium.

A 1995 federal parliamentary inquiry examined the issue of draining Lake Pedder and found the case had merit, but it was unclear if the significant costs involved in restoration would be environmentally worth it.

The inquiry's report labelled Lake Pedder's flooding as "unfortunate" and acknowledged it would not have been approved in 1995.

The 50th anniversary of the flooding coincides with the launch of the United Nations Decade of Ecological Restoration 2021–2030.

"It's absolutely critical that we adopt nature-based solutions to the climate and biodiversity emergencies that we now face," Ms Milne said.

Restore Pedder campaigners in kayaks on the lake. ( Supplied: Andy Szollosi )

"We have to get back to protecting what is left of the natural environment and restore as many forests, mangroves, peatlands, wetlands as we possibly can.

"It's a perfect coming together of global efforts in ecological restoration and putting Tasmania out there on the global stage as an icon about what is achievable on the mistakes of the past."

When asked if the Greens and environmentalists needed the Pedder campaign to stay relevant, Ms Milne said the movement was more relevant than ever — with or without the campaign.

She pointed to European parliamentary elections where green parties topped the polls in Brussels, Berlin and Dublin.

Many of the original Lake Pedder protesters are no longer alive, but for the remaining wilderness lovers who remember the old Pedder the draining would heal old wounds.

"For the broader community it is really that notion that it is possible to undo the extremes of the past and give the next generation hope that we can actually build resilience into ecosystems," Ms Milne said.

Lake Pedder feeds into the Gordon Dam. ( Supplied: Angela Wilson )

Making the case

With failed attempts hanging over them, the campaigners are determined to get their case right.

A large kayaking event is planned for February 2020 as the organisers ramp up efforts to raise awareness to the cause.

Restore Pedder has recently raised $20,000 to fund advice from engineers, energy experts, and economists to model dam removal scenarios by June.

"We will provide all of the evidence that is required," Ms Milne said.

"We will need a strong restoration management plan, so that looks at science issues and all of the flora and fauna issues and the prospects of the area revegetating naturally or whether it would need re-seeding."

While Lake Pedder does not have any energy assets attached to it, it makes up 42 per cent of the inflows to Lake Gordon, which powers the Gordon Power Station — Tasmania's largest.

The combination of the two lakes is the largest storage of water in Australia.

Lake Pedder provides 515 gigawatt hours of energy every year, and removing that amount of power from Tasmania's grid would have ramifications.

Ms Milne pointed out Lake Pedder's contribution was about the same as the new 48-turbine Cattle Hill Windfarm in the Central Highlands.

"It's not much in terms of what you'd need to replace the energy," she said.

Combined, Lake Gordon and Lake Pedder make up the largest water storage in Australia. ( Supplied: Hydro Tasmania )

A major industrial like TEMCO reducing its demand in the state would also neutralise the energy need, Ms Milne said.

It is unclear what the draining of Pedder would mean for Scotts Peak Dam, Serpentine Dam, and Edgar Dam.

Energy Minister Guy Barnett said draining the lake would have significant impacts upon environmental, social, and economic values.

"Lake Pedder is vital for Hydro Tasmania's renewable energy infrastructure, contributing around 40 per cent of the water used in the Gordon Power Station and powering more than 50,000 homes and businesses each year," he said.

"Lake Pedder plays an important role in maintaining Tasmania's energy security as we approach our nation-leading target to be 100 per cent self-sufficient in renewables and deliver the lowest energy prices by 2022.

"Renewable energy is one of Tasmania's largest economic opportunities for the next decade, with our Battery of the Nation pumped hydro plans, new wind farm projects and the second interconnector set to create thousands of jobs and billions in investment for Tasmania over the coming years."