Anglers who fish without a rod licence are facing a crackdown by the Environment Agency's Thames region.
The blitz will involve more than 20 enforcement officers making spot checks at lakes, rivers and canals to inspect anglers' rod licences this weekend.
Anyone found without a licence could face a £2,500 fine.
Over the past 12 months, enforcement officers in the region have checked more than 17,000 licences.
A total of 800 people have been convicted of fishing without a valid licence, and fined.
Regional fisheries manager Darryl Clifton-Day said: "Rod licence evasion means less income to improve our fisheries and ultimately less quality fishing opportunities for anglers on the banks."
During a national three-day blitz last year, 11,851 checks were made, and 989 anglers were later prosecuted.
There are 17,000 post offices that sell licences.
They can also be obtained by calling 0870 1662662 or through the agency's website at www.environment-agency.gov.uk/fish
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