Hundreds of eels and fish have been killed due to contamination of a creek running through South Hagley Park in Christchurch.
A blue tinge to the creek was reported on Saturday evening.
Canterbury Regional Council says it is likely that the pollutant reached the stream after someone tipped waste down a stormwater drain or through an accidental spill.
The council would like to hear from anyone who saw any suspicious behaviour near the stream or on an industrial or commercial site near the park.
