A Bay of Plenty rūnanga says it is disappointed the region's council never informed it that Fonterra had spilt 11,000 litres of whey into the Rangitāiki River last year.
The dairy giant was fined over $170,000 on Friday for polluting the river through four failures of its wastewater irrigation system, and two overflows into the stormwater system.
The whey washed into the river from Fonterra's Edgecumbe plant between September and April but Te Rūnanga o Ngāti Awa says it first heard about it on Monday morning.
The iwi authority's chief executive, Enid Ratahi-Pryor, said she found out about the spill through Te Manu Korihi.
"We're very disappointed that not only did we not get notification of this, nor did we even get a media release. So we're reading the media release second-hand.
"We're not very impressed with the fact that it's media advising us of these issues."
Fonterra said it did engage with Te Rūnanga o Ngāti Awa, but the iwi said Fonterra must have only told its commercial arm, Ngāti Awa Group Holdings Ltd, and not the iwi authority, because they had no idea the spill had occurred.
The Crown has acknowledged the river is of cultural significance to Ngāti Awa, and Ms Ratahi-Pryor questioned why the regional council did not inform them of the spill.
"Do they take their relationships with iwi seriously enough to have these proper systems in place? What this currently says to me is there is a problem and obviously we'll be following this up with the regional council."
"Our expectations are as a treaty partner we need to be advised about these things."
Ms Ratahi-Pryor said, even though the whey had been flushed out of the river, the spill had a deep spiritual impact on the whanau.
The Bay of Plenty Regional Council said it was not contacted by Fonterra about the spill until two days after it happened, and did not notify the iwi because it had already washed down the river.
The council's deputy chief executive, Eddie Grogan, said the call not to inform the iwi was made by the officer who attended the spill site.
"Because there wasn't anything further that could be done at that time, the officer made a decision not to provide further information.
"Had there been a bigger effect or some further clean-up, then a different decision may have been taken."
A Tauranga iwi also had a communication issue with the Bay of Plenty Regional Council earlier this year when the council failed to notify it about an oil spill.
However, Mr Grogan said they have learnt from that incident.
"It depends very much on the iwi groups, so in Tauranga we now have a very, very clear protocol about who to call and when and how they want their information.
"In other areas we don't have those established at the moment and it's a learning process for us. We will be having a talk to Ngāti Awa about timeliness in terms of our advice to them and exactly what information they want."
Mr Grogan said the rūnanga told them it was pleased the council took Fonterra to court but wanted a system in place so they could be notified in future.
Te Rūnanga o Ngāti Awa said this incident felt like a backward step in its relationship with the council, and it would be meeting with them to prevent this happening again.