Anglers are being asked to help stop the spread of "killer shrimp" after its discovery in the Trinity Broads - with the organisation who owns the waterway revealing there "could be millions already".
Killer shrimp are named after their voracious eating habits, and prey on damselflies, water boatmen, freshwater shrimp and fish eggs and fry. They were recently found in Rollesby and Ormesby Broad by warden Eilish Rothney who works for Norfolk Wildlife Trust.
Helen Jacobs, senior conservation advisor at Essex and Suffolk Water, which owns the majority of the site, said Ms Rothney's discovery was "heart-breaking".
"Killer shrimp have been found in the Norfolk Broads waterways before, but this is the first time we've discovered them in Trinity Broad," she said. "The area is a Site of Special Scientific Interest, so wildlife could be seriously impacted.
"Once you've got killer shrimp you can't get rid of them. Even though we caught them early, there's already millions of them. They're extremely hardy, and breed like crazy.
"In fact, they're so resilient, they can live in the folds of your clothes for up to two weeks."
Ms Jacobs said the key now was to "stop them spreading further".
She said: "There are temporary fishing bans while we get the situation under control, and we're working with our partners at Trinity Broad to get signage and wash-down stations in place for anglers and sailors.
"It's important that people check, clean and dry all their equipment before they come to, and then leave, Trinity Broad. We're relying entirely on the goodwill of the people to respect what we're asking of them here."
Simon Crutchley, who lives in Rollesby and frequents Trinity Broad almost daily to see the cygnets, said he was "alarmed" by the "catastrophic infestation".
He said: "Anyone who loves wildlife would have been shocked to see the warning signs stretched along the fishing platform.
"It's terrifying. You could carry the killer shrimp elsewhere just by sticking your wellies or net in the water, and then forgetting to decontaminate them."
Ms Jacobs speculated that the shrimp were brought to the broad over lockdown, possibly through illegal recreational fishing or swimming.
She said: "Luckily, Trinity Broad is muddy, and killer shrimp love gravelly surfaces. So far, the shrimp are concentrated around Rollesby Bridge. We need anglers to keep a 5m distance from that point to stop them spreading further."
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