The contamination of a Taranaki stream which has killed more than 1000 fish is being linked to a chemical spill at a meat processing plant.
Staff at the Silver Ferns Farms plant in Hawera were evacuated on Wednesday afternoon after an ammonia leak.
Cordons were put up around the plant and nearby residents were asked to close their windows, stay indoors and avoid using air conditioning.
The Taranaki Regional Council said it was alerted to a potential fish kill in the Tawhiti Stream on Friday afternoon, likely linked to the earlier emergency at the upstream Silver Ferns Farms plant.
The Tawhiti Stream flows into the lower Tāngāhoe River.
It said investigations showed it was a significant event, with more than 1000 fish (mainly eels) dead or dying.
Local iwi has issued a rāhu and the South Taranaki District Council had put up public health warning signs.
The regional council said heavy rain on Friday night flushed the stream and any impacts on the Tāngāhoe River were being assessed.
It said Silver Fern Farms was fully cooperating with the council's investigation and dealing with public inquiries.