Bailiffs are patrolling rivers and lakes in Bedfordshire, Buckinghamshire, Cambridgeshire and Norfolk checking if anglers have a valid rod licence.
It is the closed season on rivers until 15 June but some lake fisheries are open and anglers need licences, the Environment Agency said.
Ian Hirst, from the agency, said: "Anyone found fishing without a rod licence will receive an offence ticket.
"They could also end up in court."
"The coarse fish close season on rivers runs until 15 June so no one should be fishing on them until then," he added.
Fisheries staff are carrying out essential work such as surveying, disease control, restocking and habitat improvement at present.
But they also carry out enforcement and are patrolling waters across the East, Mr Hirst said.
"People who don't buy a licence are cheating their sport and other anglers," he said.
"Anglers must be in possession of a licence before fishing and must be able to produce it when requested by an Environment Agency bailiff or other authorised person."