The Snowy Mountains Scheme in far south-eastern New South Wales will be formally declared a National Heritage Place as part of a public event in Cooma today.

The scheme will become the 107th place on the list, joining icons like the Sydney Opera House, Bondi Beach and the Great Barrier Reef.

The scheme includes nine power stations. ( ABC News: Adrienne Francis )

The listed area includes 15 major dams, nine power stations and a pumping station, covering a mountainous area of 4,600 square kilometres.

Though listing will not restrict operations, with the scheme currently supplying more than 30 per cent of all renewable energy to the mainland electricity grid.

Former worker Margret Dowd left Germany as a young teen, after her father was recruited to work on the scheme.

"We are all so proud and when I heard that I was blown away," she said.

"We came so far, and not just us, there were Norwegians, Swedish and Italians too.

"We all came to Cooma and we are very, very proud that were were part of the scheme."

A melting pot in the mountains

Margret Dowd (L) and her family all worked on the scheme. ( Supplied: Margret Dowd )

An estimated 100,000 workers were employed during the 25 years of construction of the Snowy Mountains Hydro-Electric Scheme between 1949 and 1974.

The majority were migrants from more than 30 nations, creating a cultural melting pot across the New South Wales Alps.

"People that came from war-torn countries were able to identify with building this nation by being given productive work," 77-year-old retiree Wally Burton Mills, who still lives in Cooma, said.

Mr Mills said he was recruited to work in the Cooma Snowy Hydro office as an electrical engineer in May 1959.

Ms Dowd still lives in Cooma today. ( ABC News: Adrienne Francis )

"It was at the forefront of world development to apply such high voltage equipment to make it economical to transfer huge volumes of electrical energy over hundreds of kilometres," he said.

Ms Dowd said she still remembers what the area was like when her family first arrived.

"When I was 14 we came to Australia and went to Adaminaby and my experience there was like I was coming to a wild west town," she said.

"The (horse) hitching rails were on the side of the road and we would walk on board walks."

Ms Dowd later began working on the scheme in 1955 as an administrative assistant.

Snowy Hydro Upper Tumut area manager Kent Allen said it was easy to see why the scheme was built in the high country.

"We see snow in most months of the year," he said.

The scheme collects, stores and diverts water in the Snowy Mountains through 16 major dams, seven power stations (two of which are underground), and 225 kilometres of tunnels, pipelines and aqueducts.

It also diverts thousands of mega litres of water west for irrigated agriculture worth more than $3 billion.

"It is the largest hydro electric scheme in Australia, that is still the case," Mr Allen said.

"They weren't just built as power stations, actually they are a thing of beauty."

Lower Snowy River badly neglected: conservationists

But conservationists said there was still unfinished business, describing progress to restore the degraded lower Snowy River with environmental flows as "woeful".

"We can't overlook the terrible downstream impacts," Jonathan La Nauze, from the Australian Conservation Foundation, said.

The scheme remains the largest hydro-electric project in Australia.

"The Snowy River these days is surviving on about 11 per cent of the water it used to have. Imagine if you had 90 per cent of your blood flow taken out.

"That's what the poor Snowy has to survive on."

But the Australian Conservation Foundation also said the project's important human and historical significance was in no doubt.

"We are a mature nation and we can recognise the good things that have come from the Snowy Scheme without losing sight of the work we still have to do to address the negative impact it has had on the environment in downstream communities," Mr La Nauze said.