An unannounced blitz on illegal fishing saw 40 offence notices served during the bank holiday weekend.
The Environment Agency operation focused on anglers using still waters in the east of England and took place over four days between Friday 24 May and Monday 27 May.
Officers visited fisheries in Norfolk, Suffolk, Essex, Cambridgeshire, Lincolnshire and Northamptonshire. Each location was chosen to specifically target waters with high evasion rates from previous years.
The purpose of the visits was to ensure anglers were fishing with a current rod licence and enforce any breach of byelaws which may occur.
Lesley Robertson, Environmental Crime Team Leader, said: “504 anglers were seen by our Officers, and 40 offence notices served for rod licence or byelaw offences.
“That means 8 per cent of the anglers seen were given offence notices, meaning the blitz was successful in targeting illegal hot-spots.
“These unannounced spot-checks are a good way of maintaining our vigilance against illegal fishing. We urge anybody who sees anything suspicious to contact us immediately on 24-hour incident hotline number 0800 80 70 60.”
Tom Howard, Fisheries Intelligence officer, added: “The law-abiding anglers were very happy to see our officers out on the ground and were encouraged by our continued stance against illegal fishing.
“Although we know certain areas to target, we rely on anglers and the general public to provide information which guides us to sites we may not be aware of.
“These types of incident can be very damaging to river fisheries and if nets or traps are left unattended, they can cause damage to other wildlife as well.”
Anglers are reminded that the fishing closed season applies to all rivers, streams and drains between 15 March and 15 June. However, most still waters and canals do not have a closed season.
All anglers need a valid Environment Agency rod licence which allows them to use up to two rods. Rod licences run from 1 April to 31 March and fishing without one can lead to a substantial fine.
Anyone caught without a valid rod licence can expect to be prosecuted and face a fine of up to £2,500.
To help crack down on unlicensed anglers report illegal activity to 0800 80 70 60. You can also contact Crime Stoppers anonymously on 0800 555 111.