Anglers in south Lincolnshire are being reminded rivers are off limits from Sunday.
The Environment Agency is warning anyone thinking of going fishing in rivers and drains that the coarse fishing close season is in place and anyone caught breaking the rules may be prosecuted.
Fishing is still permitted on many canals and stillwaters, depending on landowner agreement.
James Finch, enforcement team leader, said: “The river close season for coarse fishing is there for a reason.
“By preventing coarse fishing for three months, between March 15 and June 15, it allows for an uninterrupted spawning period which increases spawning success, in addition to providing wider environmental benefits.
“Our enforcement officers will be carrying out regular patrols of waters during the close season and anyone found fishing illegally may face prosecution, and a hefty fine.”
All anglers need a valid Environment Agency rod licence which allows them to use up to two rods. Licences run from April 1 to March 31 and fishing without one can lead to a fine of £2,500.
James added: “The money raised through the sales of rod licences is re-invested and enables us to improve all fisheries including rivers for anglers.
“Our officers routinely undertake licence checks and we urge anyone with information about illegal fishing activities to contact us.”
Illegal fishing should be reported to the Environment Agency’s incident hotline on 0800 807060.