Conservation Minister Kate Wilkinson has been criticised for refusing to take part in a court action that will have a dramatic impact on waterways.

Fish & Game chief executive Bryce Johnson said he had urged her to make sure the ministry was represented in a High Court appeal by Federated Farmers and Horticulture NZ against a recent landmark Environment Court decision on reducing water pollutants.

She had been involved in the case before the Environment Court decision on Horizons Regional Council's One Plan, Mr Johnson said, and he told her she needed to stand firm against the latest appeal.

He sent emails to this effect on October 4 and October 9. Ms Wilkinson had not responded other than to acknowledged receipt, he said.

In the emails, released by Fish & Game under the Official Information Act, Mr Johnson said the court's decision was undeniably an "extremely significant case for biodiversity on private land, sustainable land use and conservation in relation to public water bodies", and "it is essential that you are represented at the High Court".

He said it was "manifestly unfair" that the burden of defending the court's decision would fall on Fish & Game, a non-profit organisation.

"DOC has a clear statutory obligation to advance conservation, and the minister's absence before the High Court will inevitably attract substantial public and political criticism if you fail to appear in this case," Mr Johnson wrote.

A spokeswoman for Ms Wilkinson said she had made the decision not to join the appeal "on advice from the Department of Conservation".

"The High Court has been asked to determine questions of law.

"The minister is comfortable with leaving these issues to the other parties involved.

"The minister may become involved again should the High Court refer any matters back to the Environment Court."

The Environment Court ruling in August would allow the council to limit the amount of nitrogen applied to land used for dairying, intensive sheep and beef farming and horticulture in the Manawatu and Whanganui catchments.

The ruling was hailed by environmentalists as it would reduce the amount of runoff to waterways and was likely to set a precedent for other councils.

Federated Farmers and Horticulture NZ appealed last month, saying they felt the ruling had "gone too far" and would threaten the livelihood of some farmers.

They felt the court had made an error in law.

ONE PLAN TIMELINE

2003-07: Consultation on draft plan

May 2007: Proposed One Plan notified

2007-10: Further consultation

2008-10: Council hearings

August 2010: Hearings panel decisions issued. More than 20 appeals lodged

2011: Further consultation and mediation

2012: Environment Court hearings

September 4: Environment Court decision released.

September 25: Decision appealed to the High Court by Federated farmers and Horticulture NZ.

October: Ravensdown and Fish & Game file notice to be party to the appeal, meaning they can be heard at the hearing, which is likely to be in Wellington or Palmerston North early next year.

- © Fairfax NZ News