The Environment Agency is investigating after thousands of fish were found dead on Skitwath Beck near Penruddock in North Cumbria. It's believed a slurry leak from a nearby farm is the cause.
The beck has been loving nurtured by a local resident over 10 years, who has created habitats that have increased fish populations. He was horrified at finding huge numbers of those fish were dead.
The slurry has now mostly washed through and the Environment Agency says it's not causing any more damage.
But Local anglers are concerned it will take years for this habitat to recover.
The farm has been located and the Environment Agency is considering if any further action needs to be brought against it, but it warns other land owners to be extra careful to make sure it doesn't happen again.