Dead fish have been reported floating in a pond in a Preston park.
The fish, believed to be carp, were seen at the Serpentine Lake in Moor Park.
The incident was reported to the Environment Agency, and a local councillor said he was concerned something had contaminated the water.
Deepdale Independent councillor Terry Cartwright said: “I got a message from a resident who said he had been around the duck pond and there were several fish floating.
“He described them as carp.”
Coun Cartwright said: “I’m concerned that something has got in there that’s killing fish and other wild pond life.
“Obviously something has got in there that’s affected the pond life, and I hope the Environment Agency can tell us what it is.”
He added that he was worried pets could be harmed if there was something affecting the water.
He said: “You can walk dogs right up to the railings and there is a foot path all the way around which leads to the play area. I would say a dog could easily get to it.
“The front of the duck pond is railings, but as you walk around the side of it there’s just a metal railing so anything can get under it.
“There could be something in it that’s harmful to people’s pets because it kills the fish.”
A spokesman for the Environment Agency said the deaths may have been caused by “water quality issues”.
He said: “We were called to Moor Park in Preston following reports of dead fish found in a lake. An initial assessment indicates that this was caused by water quality issues.
“We are providing advice and guidance to the local authority, which is responsible for the management of the lake, and will continue to support them should we be required.”