An Australian National University review into the environmental water flow agreement for the Snowy River has found the annual target has not been reached once in its 20-year history.
For decades the Snowy River was diverted for the Snowy Hydro Electricity Scheme, but eventually years of local campaigning led to a commitment to restore environmental flows.
It took three governments to sign 2002's historic Snowy Water Inquiry Outcomes Implementation Deed.
Jamie Pittock, one of the three authors of the review recently published by the CSIRO, said the annual targets had never been reached.
"The findings are rather sad," Dr Pittock said.
Dr Pittock said the lack of a single government agency being responsible for meeting the targets was a major problem.
"Unlike with the Murray-Darling Basin, nothing like that exists in NSW for the Snowy," he said.
"We're still operating on what we understood 20 years ago to be best practice, which isn't now, and the deed has no provisions to manage the impacts of climate change."
'So hard to track'
Snowy River Alliance president Vickii Wallace said the review showed the agreement lacked transparency and was inadequate.
"It's shocking," she said.
"It's just so complicated, and intentionally complicated — it's just so hard to track."
Ms Wallace said the water released by Snowy Hydro following heavy rain this summer, which led to flooding around Lake Jindabyne, should be separate to the environmental flows.
"Water released in December and January — that's actually been taken off this year's environmental allocation," she said.
Snowy Hydro chief executive Paul Broad said company set aside water in Lake Jindabyne for environmental flows.
"We've been holding the lake a little bit higher to maintain our environmental flows in the drier times," he said.
"We are constrained somewhat in our licence about when and how much we release, but the flows are meant to represent what mother nature's doing.
"We are trying to balance up all the relating demands on us."
'Big arm-wrestle'
The Snowy River Alliance is calling for a significant review into the deed agreement.
"We've been waiting for too long to get a credible delivery for the Snowy — the NSW Government needs to go back and have a look at it," Ms Wallace said.
"Every drop of water is so precious to make electricity, so it's quite a big arm-wrestle, but it just deserves a bit more honesty."