Rare British crayfish are being introduced back into Somerset's rivers as part of a breeding programme to help save them from extinction.
The white-clawed crayfish are under threat because their bigger North American counterparts compete for food and carry a plague deadly to the UK species.
The elusive creatures are related to the lobster, hide under rocks and only emerge to scavenge for food.
But the American species are now thought to be found in 80 per cent of the UK's rivers, leaving the smaller British crayfish to go hungry.
Studies have shown that the British crayfish population has decreased by 70 per cent - and could become extinct within 20 years.
Breeders at Bristol Zoo have reared 80 crayfish for a year and will now reintroduce them to the wild.
The project has been organised by the Environment Agency, which hopes to boost crayfish colonies in the region.