Dead fish floating in Awahou stream, near Windsor Park, Hastings

About 20 dead fish were found in the Awahou Stream, near Splash Planet, in Hastings, on Wednesday. Photo / Warren Buckland

About 20 fish have died in mysterious circumstances in the Awahou Stream near Windsor Park in Hastings.

Hawke's Bay Regional Council group manager policy and regulation Katrina Brunton confirmed council had been notified of the dead fish on Wednesday.

About 20 dead perch and goldfish, measuring about 15cm-long were found floating in the pond area - no native fish or eels were found dead.

Water quality, acidity and toxicology levels all came back clear meaning the cause of death for the fish is unknown. Photo / Warren Buckland

"There were many other fish in the pond alive and healthy."

Burton said water quality testing showed the water to be clear, with neutral acidity levels and a regular temperature.

There was no sign of any toxins or poison.

"At this stage the cause of death of the fish is not known."

Perch are an introduced pest species in New Zealand, and the council did not know when they were put in the pond, Brunton said.

Anyone with information is asked to call the regional council's 24/7 pollution hotline 0800 108 838.