Fonterra has been fined over $170,000 for polluting the Rangitāiki River, which the local regional council says is a significant taonga for iwi.
Fonterra pleaded guilty to all of the six charges which the Bay of Plenty Regional Council brought against it after four failures of its waste water irrigation system and two overflows into the storm water system.
Council pollution prevention manager Nick Zaman said the 11,000 litres of whey dumped into the river was deadly for fish.
"It depletes oxygen levels which means that it can have an adverse affect on the fish.
"The river is not only important because of its indigenous fish population, that it's the spawning site for whitebait, but it's also very culturally significant to a number of iwi and the Rangitāiki is very much a river of significance for them."
He said it is the pātaka kai for the Ngāti Awa, Ngāti Tūwharetoa, Ngāti Whare, Ngāti Manawa and Ngāi Tūhoe iwi.