Invaders can destroy native species
Wildlife "invaders" which can threaten native species have not worked their way into rivers in the Isle of Man.
The Government Laboratory has used a new biocontamination index to check whether Manx rivers contain mainly native insects, snails and crustaceans.
More than half of Manx rivers showed no biocontamination at all, while less than a third showed harmless invaders.
Creatures including Chinese mitten crab and the North American signal crayfish have caused damage in the UK.
They can destroy native species and damage the environment.
John Shimmin, local government and the environment minister, said: "It's great to be certain that our streams and rivers are currently free from animal invaders, such as signal crayfish and Chinese mitten crabs.
"These animals are incredibly destructive and it's essential that we avoid their introduction here on the Isle of Man.
"The Government Laboratory has been contacted many times recently by people wanting to import signal crayfish - and it's vital that they don't."