The Waikato Regional Council has identified the source of contamination which killed fish and eels in a creek.
Last week resident Eowyn Starr pulled out a bucketful of dead eels and kokopu from a stream running through her Paeroa property and said the water had turned pink and opaque.
The council said the last of the contaminant in the 220m-long stream had been removed and there was no further risk to the environment.
It said identifying the chemical was now the subject of an investigation which could take months to complete.
The council has reminded people to be careful when using chemical products to ensure they are not inadvertently discharged.