Farmers are being warned to take care over sheep dipping - to prevent crayfish from being poisoned.
A mailing campaign has been launched for farms near the River Kent and parts of the Rivers Leven and Eden.
Earlier this year several thousand white-clawed crayfish were killed in two separate pollution incidents in the River Lyvennet and River Mint.
The Environment Agency is warning farmers to take extra care with sheep dip chemicals.
Jonathan Shatwell, the agency's environment manager for Cumbria, said: "These crayfish are very sensitive to a range of pollutants, including those released from sheep dipping and similar activities.
"Pollution from sheep dip is a national problem but in Cumbria prevention is especially vital because of the risk to the white-clawed crayfish."