A river that was covered by a thick layer of foam two months ago will be restocked with 3,000 fish as part of an ongoing restoration effort.
The substance coated an “extensive” stretch of the River Thet in the centre of Thetford, Norfolk, in October, killing up to 1,000 juvenile fish and fry.
The Environment Agency said it would release a mix of native one-year-old species, including roach, dace and chub, into the river on Monday.
The organisation has been investigating the source of the pollutant and said reintroducing fish at two sites was key to helping the river return to “full ecological strength”.
“Specialist teams have carried out extensive water-quality testing and ongoing monitoring will continue over the coming months to track fish survival rates and river recovery,” it added.
The River Thet is a globally-rare chalk stream, with almost a third of the world’s chalk streams found in the East of England.
Thetford River Group, a local preservation collective, said the foam substance covering the river in October followed a similar issue in December 2024 and called for any perpetrators to be detected and prosecuted.
The Environment Agency said investigations of this type were complex and time-consuming and typically took many months.