Anglers fishing the River Waveney and Oulton Broad are being urged to ensure boats and tackle are dried out afterwards so they don't help a deadly crayfish disease to spread.
Thousands of dead Turkish crays have been seen in the river and broad over the weekend.
Environment Agency spokesman Amanda Elliott said tests had confirmed an outbreak of Aphanomyces astaci, commonly known as crayfish plague.
Measures are now being put in place to try to prevent any spread, particularly to rivers populated by the British white-clawed crayfish, such as the upper Waveney and the nearby Yare and Wensum.
Ms Elliott said: ``The affected animals are Turkish crayfish. What we most concerned about is preventing the disease spreading to another river system.
``Luckily, there are no British white-clawed crayfish recorded in the River Waveney.''
Thousands of dead Turkish crays have been seen in the river and broad over the weekend.
Environment Agency spokesman Amanda Elliott said tests had confirmed an outbreak of Aphanomyces astaci, commonly known as crayfish plague.
Measures are now being put in place to try to prevent any spread, particularly to rivers populated by the British white-clawed crayfish, such as the upper Waveney and the nearby Yare and Wensum.
Ms Elliott said: ``The affected animals are Turkish crayfish. What we most concerned about is preventing the disease spreading to another river system.
``Luckily, there are no British white-clawed crayfish recorded in the River Waveney.''
