Stort Valley Angling Society, which manages Netteswell Pond on behalf of Harlow Council, is so alarmed at the illegal activity that it has contacted police and the Environment Agency.

Although the pond, which is stocked with carp and bream, can be fished during the day, volunteer pond officers have discovered groups of men. some of whom are believed to be from eastern Europe, fishing there at night which is not allowed.

At other times groups have been found fishing without the required Environment Agency licence. Last month 10 men from the London area were arrested and on one occasion a bag of gutted fish was found in a nearby car park.

"These groups are coming down at night and stealing the fish," he said. "It is a problem throughout the country although it has only just hit us. It costs quite a lot of money to restock the pond."

Society vice-chairman Gordon Weemes said he recently came across a Lithuanian man fishing at the pond with a knife.

"Where they come from they fish, they catch them and eat them. They need to be educated about it."

Essex Police wildlife and nature crime officer PC Rob Hance told the Star: "From what the findings are it is predominantly eastern European people that are fishing the pond.

"Though it is not a personal finding of mine, they are believed to be eating the fish. We don't fish to eat but it would appear in some cultures that is what they do."

Mr Hance said it was a national problem. "It is the anglers' responsibility to find out about the laws and the responsibility of the club to ensure there is proper signage on the law , not just in English but a couple of European languages as well."

An Environment Agency spokeswoman said: "We are aware of the problem and have offered our support to carry out some patrols with the angling society."