Hundreds of fish have been killed in a stretch of the River Nene in Peterborough.
Residents living at Riverside Mead in Stanground spotted the water was a cloudy, milky colour yesterday - and today found dozens of dead fish floating in the water.
A number of fish also washed up in residents’ gardens.
It is not yet known what caused the death of so many fish - but it is feared chemicals have leaked into the river.
Residents have now contacted Anglian Water and The Environment Agency following the discovery.
One woman said they had been given no advice about the situation, with no information about drinking water and if pets should be kept away from the river.
An Anglian Water spokesperson said: “We’re responding to reports of dead fish in and around the Riverside Mead area of Peterborough. We’re working with the Environment Agency to investigate thecause and assisting with clean up actions in the immediate area.”
A spokesman for The Environment Agency said: “Our officers are responding to reports of dead fish at Stanground Lode, off the River Nene, and have been on-site since Monday, when we received the initial report.
“We are working with partner organisations to investigate potential causes, and will continue to monitor the situation.
“As always, we’d remind people to please report fish in distress or suspected pollutions to us as soon as possible so we can investigate – call our 24-hour incident hotline on 0800 80 70 60.”
The spokesman added: “We believe this is an isolated incident which is not posing further risk to the environment or a risk to drinking water.
“By the time we received the reports, the fish were already dead so there was nothing we could do. Anyone who suspects fish in distress, fish deaths or pollution incidents should report them as soon as possible, so we can investigate and have as much opportunity as possible to take the appropriate actions.
“We would normally advise people not to let their pets drink from open water, as it could contain substances – even natural ones like algae – that could make them ill. This advice still stands as we are investigating this incident.”