"We are not prepared to wait for regulation, and the outcome will be driven by farmers and achieve a better result for rivers without destroying farms or rural communities."
The Whangaehu/Mangawhero catchment is 150,000ha, with 140 farmers. Most of them have Whole Farm Plans, done under Horizons' Sustainable Land Use Initiative (SLUI).
Cranstone said "filling the holes" in those plans would be a good place to start.
The group could also ensure every farm in the catchment has an environmental plan. Farmers can support each other and "give each other the nudge".
The Whangaehu River is unusual. It starts at Mount Ruapehu's crater lake, and carries contaminants from it.
Like the Mangawhero, it runs through eroding hill country with sheep and beef farms.
The river's main challenge is sediment, Cranstone said, not the nitrates that are a problem in dairy country.
The farmers will aim to build on the water quality work Ngāti Rangi is doing further up on both rivers.
There will be new science and funding opportunities that can achieve results without being too costly, Cranstone said.
For example, starting the break feeding of a winter crop at the top of a slope can stop 90 per cent of sediment getting into the waterway at the bottom.
"There's no extra cost or reduction in crop utilisation, just some extra planning."
More poplar planting will keep soil on the hills, without reducing grazing. The trees could also earn carbon credits (NZUs), and meat raised sustainably could fetch higher prices.
Cranstone wasn't keen to see hills blanketed with pine trees.
"There's a concern that plantation forestry has destroyed a lot of our rural communities. It was planted 30 years ago and now it's destroying rural roads as it gets harvested."
He and fellow officeholders Grant Adkins and Chris Davison plan to hold meetings for all farmers every two months. They will be advertised on Facebook and moved around the region.