Alien species of crayfish have been found to be invading a West Norfolk river.
The Environment Agency has confirmed that the American Signal Crayfish has been spotted in the River Nar.
The crayfish is proving to be a great threat to native species within British waterways.
Signal crayfish were introduced to this country in the 1970s and sold to farmers looking to diversify. They went onto establish populations in rivers, lakes and ponds after a number escaped.
An Environment Agency spokesman said: “This unwanted visitor preys on native wildlife and spreads crayfish plague, a disease deadly to native white clawed crayfish.
“We ask anyone who sees a non-native species to report them to the GB non-native species secretariat.
“People should not simply try to trap or kill the invasive species.
“It is important to make sure that the methods and equipment used are safe for other aquatic animals, like otters and water voles.
“Anyone who wishes to explicitly fish for crayfish by any means, including hand-picking, can ask for permission from us.
“We have strict rules in place to protect our native white-clawed crayfish as well as controlling the spread of invasive non-native crayfish.”
To report the sighting of any crayfish you should go to www.brc.ac.uk/risc/signal_crayfish.php