Pollution is killing fish and threatening other wildlife in a Penryn river.
Members of the public are being urged to help trace the source of the pollution, which is wiping out fish from a tributary of the Penryn River.
An investigation has now been launched by the Environment Agency, after a member of the public reported that a stream running beside Greenwood Road in Penryn had turned foamy and had a strong chemical smell.
The Environment Agency traced the pollution back to a culvert that drains from the Kernick Industrial Estate, although the exact source of the mystery pollutant is still unknown.
A sample of discharge, which smelt strongly of degreasant or disinfectant and was faintly reddish-orange in colour, was sent for analysis at a laboratory.
So far there have been reports of dead fish as far upstream as Greenwood Road and downstream as far as Truro Lane.
Redwynn Sterry, from the Environment Agency, said: "Aquatic life is being killed by this pollution. It must be found and stopped. All the signs suggest we are dealing with repeated incidents - it is possible someone is inadvertently disposing of this pollutant without realising the harm it is causing. Anyone with information is urged to come forward."
Members of the public can either call the Agency's free 24-hour hotline on 0800 80 70 60 or contact Redwynn Sterry on 01208 265 079 during office hours.
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