Horowhenua Māori have agreed under a confidential deal to drop court action aimed at stopping the spraying of Foxton's wastewater onto an island in the Manawatu River.
It was signed in September and has only come to light now.
The signatories, Horowhenua District Council and Te Runanga o Raukawa, say it's confidential and have declined to release details.
Foxton's wastewater is going into the Manawatu River, but under the deal it will end up on the 350ha Matakarapa Island.
A draft of the agreement showed the council would pay the iwi about $640,000 over five years to employ an environmental manager and do fencing and archaeological work on the island.
Cr Neville Gimblett, who attended a celebratory breakfast to mark the deal's signing in Foxton on 27 September, said the signing was in public but the deal wasn't important enough to announce to ratepayers.
"It's an important agreement. The fact that we have made an agreement has certainly not been kept secret.
"We obviously didn't think it was important enough to go and shout it from the rooftops."
The island has several urupa on it, and Horowhenua and Manawatu iwi have been fighting the wastewater plan. The deal appears to create spray-free buffer zones.
Ngāti Whakatere spokesperson Robert Ketu said his iwi remained opposed to wastewater going on to the island.
The deal was signed for the council by chief executive David Clapperton.
"I am happy to say that instead of continuing to fund lawyers to argue the case we will instead work with iwi to respond to and monitor legitimate issues".
He said the correct process was "absolutely" followed.
The chief executive is authorised to sign off on operational matters involving sums under $1 million without taking it to the council.
Mayor Michael Feyen was not a signatory. He said he knew there had been a deal but not what was in it, even though he had wanted to know.
Mr Feyen has spent his year as mayor struggling Mr Clapperton who he accuses of side-lining him. A council meeting on Wednesday fell apart when, in his end-of-year speech, Mr Feyen said councillors were under Mr Clapperton's thumb.
Barry Judd, a councillor and deputy chair of the audit and risk subcommittee, said it was an operational document so the rules prevented it being shared with elected members.