Environment Agency officers are to carry out spot checks on fisheries in the north-east-of-England to make sure their licences are in order.
The licence helps to ensure that the fish are coming from a reputable supplier where all the necessary health checks have been carried out.
It also ensures that only species which are native or appropriate to the water courses are stocked.
Anyone found without a licence could face a fine of up to �2,500.
Health checks need to be carried out where fish are stocked in open waters, to prevent disease spreading to native fish.
Phil Rippon, Environment Agency fisheries specialist, said: "It is absolutely vital that fishery owners have the correct licence for stocking their waters. It not only protects the environment but makes sure new stocks are fit and healthy.
"The other good news is that obtaining a licence to stock fish is free and easy to obtain so there is no excuse for people not to have one."