Fewer than 7% of anglers across Wales were found to be fishing illegally in a bank holiday enforcement operation.
Welsh environmental body Natural Resources Wales (NRW) said its fisheries enforcement teams attended lakes and rivers across Wales over the Whitsun bank holiday weekend.
They spoke with more than 200 anglers and found 14 did not have a valid rod licence. They now face enforcement action by NRW.
Huw Davies, environmental crime team leader for NRW, said: "Looking after fish populations in Wales is one of our biggest priorities and the rules and regulations in place are there to help us do just that.
"While it was encouraging to see so many anglers following the rules it’s a shame there are some people that still choose to ignore them.
"We want everyone to be able to enjoy Wales’ natural resources and encourage anyone with an interest in fishing to work with us by purchasing a rod licence."
Those caught fishing illegally risk a criminal conviction as well as a fine.
Rod licences can be from local local post offices or at https://www.gov.uk/