In the quiet waters of Llyn Tegid, Wales' largest natural lake, the last wild population of the glutinous snail clings to existence — a fingertip-sized creature whose disappearance from every other British waterway tells the familiar story of what pollution and neglect cost us before we notice. A Welsh conservationist and his family have done what no one had done before: bred the species in captivity, cracking open a door that had been closing for decades. Now a network of zoos is building what amounts to a living archive, and within three years, the species may return to waters it once called