The Environment Agency are investigating after scores of a rare crayfish species were found dead in an Eden beck, in Cumbria.
More than 100 white-clawed crayfish are thought to have been killed by pollution infecting Scale Beck, near Appleby.
Ben Bayliss is from the Environment Agency
What is a white-clawed crayfish, and why are they so special?
The crustacean is the UK’s only native crayfish species and remains one of Eden’s more secretive inhabitants.
It is known to hide under rocks or large tree roots during the day, and appears at night to feed on plants and small creatures.
The crustacean is considered a keystone species, meaning they are a crucial part of the ecosystem, according to the Eden Rivers Trust.
Anyone who sees river pollution, or other concerning river activity, can call the Environment Agency's 24 hour hotline at 0800 807060.