An ammonia leak at a South Taranaki meat processing plant - which has killed more than 1000 fish and eels - is being described as a significant environmental incident.
The leak at Silver Fern Farms' Hawera plant last week has contaminated several kilometres of the Tawhiti Stream, which flows into the lower Tāngāhoe River
The Taranaki Regional Council would not be interviewed, but in a statement said it was alerted to possible fish deaths on Friday and an initial investigation has confirmed the spill has had a serious environmental impact.
The regional council said it had contacted Ngāti Ruanui, which issued a rāhui, and the South Taranaki District Council which had put up health warning signs.
Iwi leader Debbie Ngarewa-Packer said the ammonia had had a devastating effect.
"We got confirmed on Friday night that it was a complete kill and that the whole catchment from Lower Tawhiti Road into the Tāngāhoe River had been affected."
She had witnessed the affect herself.
"Dead eels, we saw dead eels. At that stage we were hoping there were not too many dead eels, but we definitely got a sense that something bad had gone down.
"Eels are seen as our kaitiaki, the minute something goes on with them then as an iwi we know we are in trouble."
Ngarewa-Packer said she wanted to know how the ammonia entered the stream.
After a meeting with Silver Fern Farms, she said she believed it got into the storm water system as part of efforts to contain the leak.
"Effectively what happens is the gas comes out and the emergency services apply a spray of some sort and it turns into liquid and is expelled into the storm water, and we think some may have gone over the road into the river as well."
She said the liquified ammonia is toxic to aquatic life.
"From what we've seen, it does a complete kill. It's a kind of toxin ... that gets stuck in the lining of their [eels'] lungs and kills them.
"It's something that you wouldn't want any part of your body or respiratory system. Look I am not a doctor but that is certainly the science we were told."
Ngarewa-Packer wanted assurances this could never happen again.
Silver Fern Farms declined an interview, but via email a spokesperson acknowledged that the leak had resulted in fish being killed which it regretted.
"We believe the ammonia entered the stream during the emergency and fish have died. We are deeply disappointed this has happened given our commitment to our environment and the stream restoration work we had carried out on the Tawhiti stream," the spokesperson said.
"Our focus is on the clean-up and to ensure no more harm is caused."
He said the company had met with Ngāti Ruanui and was determined to put this right.
The company could not say how the ammonia had got into the Tawhiti Stream.
"We are committed to a full investigation, but it is too early to know the cause for how the ammonia got into the stream. We will make the results of that investigation public."
The Taranaki Regional Council said Silver Fern Farms was co-operating fully with the investigation and dealing with public inquiries.
While the investigation was ongoing, the council said it would not answer questions about spill containment processes at the Hawera plant site or say whether those had failed.
The council said it was "fortuitous heavy rain on Friday night flushed the stream" and that any impacts on the Tāngāhoe River were still being assessed.