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