Investigations underway after fish die in foam layer on river Thet
An Environment Agency spokesperson has said the pollutant is an unknown substance
The Environment Agency said small dead fish have been found after a layer of foam covered the river Thet in Norfolk.
Specialist teams were sent to collect samples from the river, which flows through Thetford, on Saturday with the aim of finding the source of the pollution and preventing further discharge.
An Environment Agency spokeswoman said the source of the pollutant had been found but the foam would be allowed to reduce naturally as it was diluted by the rain.
She said: "This incident is a live investigation, and the pollutant is an unknown substance.
"We have detected the source and expect the foaming to reduce naturally as it is diluted by the rain that will increase the flow of the river over the next few days.
"Our officers have seen small dead fish and fry; this is obviously upsetting. We will survey the impacts once the pollutant has gone to assess longer-term impacts.
"Unfortunately, there isn't a method we can use to disperse the foam that wouldn't cause more pollution.
"We would still advise that people do not enter the water or allow animals to drink or swim where the foam is visible."
The spokeswoman said that there had been a previous incident of foam on the river Thet on December 23 2024 but the source had not been identified on that occasion.
Anglian Water has been asked for comment by the PA news agency.