Conservation Minister Kate Wilkinson and her department are refusing to say why they will not go in to bat for a landmark Environment Court ruling.
Horizons Regional Council's One Plan, which would see controls on farm nutrient runoff, was appealed in September by Federated Farmers and Horticulture NZ.
They believe it will threaten the livelihood of some farmers.
The plan and its progress through court has been followed closely by other regional councils, which see it as setting a precedent in dealing with runoff.
Fish & Game became a party to the appeal so they can be heard when it goes to the High Court, but Ms Wilkinson, who had been party to the original decision, did not.
Fish & Game chief executive Bryce Johnson had urged Ms Wilkinson to join the appeal as he said it was vital for future sustainable land use and conservation of public water bodies.
Ms Wilkinson said last month she had decided not to appeal after receiving advice from the Conservation Department.
A Dominion Post Official Information Act request to Ms Wilkinson to see this advice was transferred to the department as she said it was an "operational matter".
Acting deputy director general Felicity Lawrence declined to disclose the advice as it was "subject to legal professional privilege".
It was also withheld to "maintain the free and frank expression of opinion by officials".
Ms Lawrence said there was not sufficient public interest to outweigh her reasons for withholding the information.
Had the minister or department filed to be a party to the appeal they might have been at odds with Primary Industries Minister David Carter, who this week said the work done to estimate the cost to farmers of the One Plan was "woeful".
His ministry had commissioned research that claimed farm costs could increase by 22 to 43 per cent if the One Plan ruling was followed to the letter.
This is contrary to evidence put before the court, which stated they could rise by 5 to 16.6 per cent.
Mr Carter said he would be concerned about any proposed plan that could hinder profitability or productivity increases.
Fish & Game's Mr Johnson would not comment on Mr Carter's statements. However, he said he was "extremely disappointed" in Ms Wilkinson's decision not to be a party to the appeal.
"It is just of so much importance to the department's goals concerning water on private land. It really is disappointing the minister is not supporting us on this," he said.
- The Dominion Post
Is it time for authorities to introduce tougher penalties for poaching?Related story: Booby traps for poachers cost farmers