It's a complicated issue more tangled than an ancient river red gum's root ball.

But it boils down to irate irrigators demanding politicians stop the Murray Darling Basin Authority rewriting rules so water bought and paid for by entitlement holders would become an environment asset.

NSW Irrigators Council and its representative members argue the new rules proposed by the MDBA, known as Water Resource Plans, would reduce their right to access more than 2000 gigalitres that is owned by entitlement holders.

The Basin Plan sets a December accreditation deadline for the new plans, and once the Commonwealth classification is set, it is locked in law forever.

"This is die in the ditch stuff, a line in the sand," said Namoi Valley Irrigators executive officer Jon-Maree Baker.

"If it's not resolved satisfactorily, we start advocating to walk away from the Basin Plan."

It's a whopping volume of water at stake, worth more than $1 billion a year to regional economies - or nearly two-thirds of the volume set to be recovered for the environment under the $13 billion, 3250GL Basin Plan.

PEW, or Planned Environmental Water, is an element of state-based Water Sharing Plans, which are legally binding rules, applying catchment-by-catchment across the state.

The plans divide water between competing uses - including town supply, environment, and irrigation.

When NSW signed up to the Basin Plan in 2014 it committed to have its plans accredited by the MDBA by December this year.

Commonwealth accredited rules are called Water Resource Plans and NSW is the only state yet to submit its plans.

Under state-run versions of water rules, PEW was defined as all water specifically classified for environmental use by the NSW water managers.

But, the MDBA's interpretation differs significantly. It says the averaged volume of water not drawn for consumptive use, since 2012, must be classified as PEW.

And that's where irrigators' 2000GL problem comes in.

State Water Sharing Plans had set an upper limit for water extraction in each catchment, which is fixed under the Basin Plan laws, and known as Plan Limit.

But for the past decade or so irrigators haven't used all the water available to them under the Plan Limit.

Why the low usage of water that irrigators have shelled out for? They've taken a conservative approach during a decade of severe disruption.

There's been the Millennium Drought, many water trading reforms, new carryover provisions allowing water entitlements to roll-over from year to year, as well as new rules that restrict usage under certain conditions.

The issue is a concern across the state.

Ricegrowers Association president Rob Massina, representing more than 1200 members in southern NSW, called on the NSW government to ensure there would be no loss of productive water or property rights.

"From RGA's perspective, we sincerely hope this isn't an attempt to recover additional water by stealth. We need transparency," Mr Massina said.

"Any rule changes need to be transparent and agreed to by all stakeholders. It's important the NSW department and MDBA work with the irrigation sector to clarify any confusion.

"We want the Water Minister to give the matter some urgent attention, it's absolutely a significant issue for communities to be strong and prosperous."

Ms Baker said water property rights were under threat.

"This has happened by stealth. It's taking plan limit from not only irrigators, but all consumptive users," she said.

"We respect the environment's share. We need the MDBA to respect consumptive users such as towns, tourism, miners and farmers. It's a big part of regional Australia's economy."

NSW Water Minister Melinda Pavey said negotiations were ongoing and she would ensure irrigators' rights to access their entitlements were guaranteed.

"NSW Government has made it clear that we will be allowing take up to plan limits," Ms Pavey said.

"I have been told by multiple sources the level of consultation around the Water Resource Plans could have been better, which is why we need to take into account the concerns now being raised.

"We encourage stakeholders to make their views known."

NSW Senator Perin Davey, a former water policy adviser, shared irrigators' concerns over PEW. She said it was up to NSW Water to resolve the matter for their stakeholders.

"The MDBA are saying they can't resolve the issue because they haven't seen NSW's plans. NSW is saying it can't submit plans because it's restricted by the MDBA's interpretation. We need this resolved," Senator Davey said.

"Victoria have put in their draft Water Resource Plans for accreditation with provisions to test how it all works, with a 12 month sunset clause.

"I'm frustrated that NSW haven't even submitted a Water Resource Plan for the MDBA to judge. They should submit them and test the MDBA's resolve (over PEW)."

The MDBA said it would continue to consult over PEW, and would ensure the volume of environmental water isn't reduced.