A farmers' group is rejecting the notion that reducing the national dairy herd is the most effective way to make New Zealand's rivers more swimmable.

Photo: 123RF

Seven rural leaders, including the heads of Fonterra, Dairy NZ and Federated Farmers, yesterday pledged to improve river quality.

The informal Farming Leaders Group said while there had been progress in cleaning up waterways in the past decade, more needed to be done and more rapidly.

One of its members, New Zealand special agriculture trade envoy Mike Petersen, said the goal was to make rivers swimmable for future generations.

Photo: Twitter

"We've made a decision as leaders to stand up and put a stake in the ground and make sure we commit to swimmable rivers for our children and grandchildren.

"Just as we've been able to, in our childhoods, swim in rivers freely, we want our children and grandchildren to be able to do that same," Mr Petersen said.

Environmental and recreational groups cautiously welcomed the commitment, but Choose Clean Water spokesperson Marnie Prickett said more detail was needed urgently about how this would be achieved.

"This is a sign that the farming leaders are on the side of the public, who have been calling for a swimmable bottom line for a long time.

Ms Prickett said farming leaders should have a "comprehensive plan" and commit to "real, meaningful and urgent steps".

These would include strict and enforceable bottom lines of contaminants like nitrates and E coli, and a withdrawal of government support for large scale irrigation.

Greenpeace said the farming group should back the Freshwater Rescue Plan, which had already been signed up to by 16 organisations and experts.

It also wanted a cut in the dairy herd.

Fish & Game agreed, with chief executive Bryce Johnson saying if farmers were serious about cleaning up rivers, they should cut cow numbers.

"We've simply gone too far and even the Ministry of Primary Industries has been saying the same thing. We've just pushed the envelope a bit too far and we've gotta pull it back."

But Mr Petersen said achieving pristine waterways was more complex than just reducing the number of cows.

"I think that's too simplistic, and we've been very clear in saying that every community and every catchment needs to work out how they plan to work their way down the path to better water quality."

"Each community will have a different approach to how they address that."

Mr Petersen pointed out the dairy industry had spent a billion dollars in the past few years on keeping stock out of waterways.