A signal crayfish has been photographed in Wistaston Brook near Nantwich, and the legal position for anyone who catches one is stricter than most anglers realise: you cannot simply put it back

A crayfish photographed in Wistaston Brook, on the edge of Nantwich, has been identified as a signal crayfish, the invasive North American species that has been colonising English rivers since escaping commercial farms in the 1970s. The sighting itself isn't unusual, signal crayfish are now established across most of England and much of Wales, but each new confirmed location matters because it marks another stretch of water where the native white-clawed crayfish, already reduced to a fraction of its former range, is now at direct risk.

The threat isn't really competition, it's disease. Signal crayfish carry crayfish plague as asymptomatic hosts, meaning they can spread it through a watercourse without ever showing symptoms themselves, while it is close to 100% fatal to native white-clawed crayfish on contact. Once plague reaches a population of white-claws, local extinction typically follows within weeks. Signal crayfish also outcompete natives directly for food and shelter, and their burrowing weakens riverbanks, research on affected stretches has recorded bank erosion running well over double the rate of unburrowed banks.

What most anglers don't know is what the law actually requires if you catch one. Signal crayfish are classed as a species of special concern under UK invasive species regulations, which means keeping, moving, or releasing them back into the water without a licence is prohibited outright, not just discouraged. That puts anyone who nets or hooks one in a genuine legal grey zone: you can't legally tip it back where you found it. The Environment Agency's guidance is not to touch or handle a suspected signal crayfish, take a clear photo and note the exact location instead, and report it via the Agency's 24-hour incident hotline on 0800 80 70 60.

For anyone fishing South Cheshire's smaller brooks and becks this month, the practical takeaway is simple: a photo and a phone call do more good than an attempt to deal with it yourself, and reporting a sighting the Environment Agency doesn't yet have on record is a genuine contribution to tracking how fast the species is spreading, not just box-ticking.