An “ark” refuge is being created by the National Trust to help save one of the UK’s most endangered native species from extinction. The white-clawed crayfish is the UK’s only indigenous crayfish but the population has been almost wiped out because of the introduction of a bigger American species in the 1970s. The trust on Tuesday said it wanted to do its bit to help by creating the refuge in an old cattle drinking hole at the Wallington estate in Northumberland. It will move up to 100 of the crustaceans from the River Wansbeck, which runs through the estate, to the site, where it is hoped they will breed. Matthew Fitch, the National Trust ranger at Wallington, said the white-clawed crayfish was “on a knife-edge”. He added: “It’s so important we shore up the healthy populations, like the one we’re fortunate to have here on the Wansbeck, as quickly as we can to make sure it doesn’t vanish from our rivers altogether.” Fitch said the site would be a haven “but also contribute to the long-term protection of the animal, as the crayfish that are kept here can in theory be used to repopulate other waterbodies”. Populations of white-clawed crayfish have more than halved across Europe in recent decades. In the UK an estimated 70% of the population has been lost. The losses can be traced back to the introduction of the American signal crayfish, a bigger species introduced to Europe in the 1970s as a restaurant delicacy. They were deliberately introduced to British waterways in 1976 by a government that hoped they would be an export money spinner, supplying the lucrative Scandinavian market. Grants were made available for estate owners and others to take part. The consequences have been devastating for indigenous crayfish. As well as outcompeting smaller crayfish for food and habitat, the interloper often carries a plague that is harmless to itself but can wipe out other species of crayfish in weeks. The Wallington estate is, at 13,500 acres, the largest estate in the care of the National Trust. Rangers at Wallington have spent 15 months diligently taking water samples and surveying to make sure the project will succeed. The 200-year-old cattle drinking hole is fed by a spring, with the water flowing over barriers before it reaches the Wansbeck, meaning the chances of signal crayfish or plague entering are low. Around 250,000 visitors a year go to Wallington. As well as the marvellous Pre-Raphaelite artworks in the house people will soon be able to see a display tank of white-clawed crayfish in the property’s reception area. Ian Marshall, who is the Environment Agency’s national lead on white-clawed crayfish, said Northumberland had some of the best populations. “They are vital to our ecology, helping to keep our waterways clean and providing a source of food for other native species. “The Northumberland Crayfish Partnership is working hard to better protect them and this brilliant project at Wallington is one of many big plans to make 2022 the best year yet for the recovery of native crayfish across the region.”