Environment Agency officers are reminding anglers not to get caught fishing without a licence as more than 100 have been prosecuted in Yorkshire since April.
Some anglers have been fined almost £500 for not holding a valid rod licence when questioned by bailiffs.
One offender failed to pay compensation and was subsequently arrested and brought back to court. He is now serving time in prison, all for failing to pay £27 for a rod licence.
Fisheries Technical Officer for the Environment Agency in Yorkshire, Peter Mischenko said: “Judging by the results of our recent prosecutions in court, magistrates take fisheries offences very seriously.
“The revenue raised from rod licence sales is used to benefit and protect our fisheries and we will take action against anyone who is fishing illegally.
“We are continually working with angling clubs and fisheries owners to ensure that everybody who goes fishing does so legally, and is aware of the rules and regulations that protect our fish and fisheries.”
The fisheries team carries out regular blitzes on angling sites across the region and questioned 17,000 anglers last year.
Other offences included giving a false name and address to a bailiff and fishing with more than two rods whilst only being in possession of one licence.
Those who fish without a licence can face prosecution and a maximum fine of £2,500, with the potential for forfeiture of fishing equipment and even a ban on holding a fishing licence for up to five years.
Environment Agency officers are also working with local police officers to target poachers.
There are many ways in which an angler can renew their annual licence. Licences are available at Post Offices, online from the Environment Agency at www.environment-agency.gov.uk/rodlicence or by telephone on 0844 8005386.