I'm sure this is just another tabloid myth put about by right-wing rags like, er, the BBC.
Signs warning people not to cook fish from the River Severn have been erected after migrants from eastern Europe were allegedly caught poaching fish. John Roberts, from the Shropshire Anglian Federation, said the removal of the fish has become a major problem. He said he caught three Polish men with pike and a mallard in separate incidents last week. "Particularly at this of the year it is critical as the Polish dish for Christmas is carp, " he said.