Poaching and predation of fish from lakes and rivers has become a “major problem”, an anglers’ group claims.
Scores of fish, including valuable prize winners, have vanished from lakes, according to Angling Essex.
Anglers blame increasing numbers of otters preying on fish and thefts of large specimens by criminal individuals and gangs.
Nick Watkins, chairman of Angling Essex, said in the past decade, it had become a “major, major problem”.
Thom Airs, of Angling Times, said a carp in a lake “was an easy meal for an agile otter” but increasingly cormorants were settling inland to feed.
Gangs were a problem but they risked detection as the prized large fish have distinctive scale patterns and there was always the danger of them carrying disease to a new lake.
Anecdotally, anglers blamed people from countries whose culture was to catch and eat fish from rivers and lakes, but these numbers would not be large enough to make a big impact.
Mr Watkins echoed those fears and said: “The Polish Anglers Association has been doing a lot of really good work, going to schools and teaching youngsters about our laws and culture and what is acceptable.
“People need to realise that if you go to an owned lake and you take a fish, it’s theft.”
Predation by animals was deemed the more likely culprit, although theft could still have a serious impact.
“Fishing lake owners are reluctant to discuss loss of fish as their businesses rely on reputation,” Mr Airs said.
“Their lakes could be home to specimens that have grown large over 30 or 40 years and a loss could deter anglers.”
Mark Iley, from Essex Wildlife Trust, said: “Both otter and cormorants eat fish and at times come into conflict with anglers and fishery owners.
“Both species are sometimes wrongly implicated in the loss of fish – in general otters eat relatively small fish including minnows but can tackle fish up to several pounds.
“As an angler myself, enjoying [other] wildlife is part of the whole experience of fishing.”
The Environment Agency said: “We are not aware of any recent incidents of carp poaching on Essex rivers, but if anyone sees fish being taken illegally then they should contact us.”
An Essex Police spokesman said they take the issue “very seriously”.
“Essex Police showed its commitment to combating fish theft and illegal fishing in 2014 by signing up to Operation Traverse, which aims to protect the county’s fisheries,” he said.