Signs and fencing blocking off fishing platforms in Rollesby Broad after the discovery of killer shrimp have been torn down by vandals for the third time.
Killer shrimp - named for their voracious eating habits - were found for the first time in Trinity Broad in November last year by warden Eilish Rothney.
They prey on damselflies, waterboatmen, freshwater shrimp and fish eggs. Once they have infested a habitat, it is very difficult to eradicate them.
According to Ms Rothney it could be the case that millions had been breeding for up to two years before their discovery.
Temporary barriers had been put in place around Rollesby Broad until Norfolk Wildlife Trust (NWT) - and the organisation which owns the water way, Essex and Suffolk Water - could get a more long-term action plan in place.
But vandalism made it all the more difficult to contain the spread, explained Ms Rothney.
She said: "The netting and fencing was chucked in the Broad over Christmas. At the moment I'm short of manpower to put it all back, but for the meantime we've introduced more robust signage.
"So far we don't think the shrimps have spread to Ormesby Little or Filby Broad, but this is entirely dependent on the goodwill of anglers.
"We won't be able to stop it spreading through the system eventually, but we can slow the process. We're hoping to do this through monthly monitoring, signage and the setting up of three wash stations so anglers can keep their equipment clean.
"This is important because the shrimp can survive for over two weeks on your clothing."
She added: "For now, we're asking people not to fish from Rollesby bridge and for boats not to travel between Rollesby Broad and the other Broads."
The plan, she said, was hopefully to have these restrictions lifted by late February.
Simon Crutchley, a Rollesby resident, said he was hopeful that careful management would stop the shrimp spreading.
He said: "It would be preferable for fishermen to take notice of the signs and fish sensibly with clean equipment rather than for the NWT to have to block off the accessible platform at Rollesby as was the case first time.
"This had the detrimental impact of stopping birdwatchers or families enjoying the space too."
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