Bailiffs have been visiting anglers around South Yorkshire to ensure they hold correct fishing licences.
The Environment Agency, which carried out the operation, said 20 anglers were questioned at locations around the county and one will be pursued for offences.
Across Yorkshire as a whole, 23 people were caught fishing illegally after bailiffs visited 35 sites and questioned 367 anglers.
The blitz has prompted enforcement officers to repeat their advice for anglers to make sure they have a rod licence, otherwise they will be caught and prosecuted.
Peter Mischenko, fisheries technical officer for the Environment Agency, said: “We are out in all weathers checking rod licences and we work with angling clubs and the police to protect our fisheries.”