Migrants entering the UK from Poland and eastern Europe are poaching coarse fish which is pushing some stocks to the point of collapse, an angling association claims.
The National Association of Fisheries and Angling Consultatives (NAFC) told the BBC that the poaching of larger fish from lakes combined with two years of extreme weather had hit fisheries.
The angler and MP Martin Salter told the BBC: "Poles and eastern Europeans, in particular, have been seen and occasionally caught removing all species of coarse fish, roach, bream and perch."
Salter claims that the problem is getting worse and that the legal framework is not strong enough to cope with the problem.
"For example, in the Thames region it is legal, even though it's not in our culture, it is legal to take two fish of any size.
"In some other regions you can take as many fish as you like, but there are certain size limits. And these things are simply not enforced", he was reported as saying.
The long, hot summer of 2006 and the floods in 2007 have placed fish stocks under pressure by disrupting spawning and creating poor conditions for the growth of fry.