FISHERMEN have solved the mystery of what happened to all the fish in their lake after finding a family of very fat otters.

Ian Bouttell and Paul Atkinson say the return of a substantial otter population is causing problems for fishermen across the country.

The pair have fished a Tata Steel-owned lake, known as The Stell, at Coatham Marshes nature reserve in Redcar for carp for years but noticed a dramatic decline in numbers.

One night they stayed out all night and saw a pair of otters playing in the river. The otters led the fishermen down the lake away from their holt, or nest, but later the fishermen discovered the otters had young.

Paul Atkinson and Ian Bouttell both called for the Environment Agency to manage the otter population. They pointed out that fishermen must pay the agency for the right to fish but argue fishing is not protected.

Mr Bouttell said: “I would say there’s no fish left in there at all. There’s rare birds in the marshes and it wouldn’t surprise me if they went after them too. Some of the carp were 40 years old.”

He said it would be very difficult and expense to install an otter fence and restocking the lake the lake would cost thousands of pounds.

Coatham Marsh Nature Reserve is owned by Tata Steel, but managed by Tees Valley Wildlife Trust. Jeremy Garside, chief executive of the Trust, said otters had not been deliberately reintroduced but had come back to the area naturally as rivers became cleaner.

He said: “Otters were pretty close to extinction and we didn’t have a confirmed siting on the Tees until 2002. It’s a good, natural process that they’re recovering naturally and we all have to learn to live with them again.”

Peter Barnett, secretary of the Tata Steel Angling Club which manages The Stell, also known as The Fleet, said he had been alerted to the problem but so far the club had not been able to find the otters.

A spokesman for The Environment Agency confirmed the otters had not been deliberately introduced. A spokesman for Tata Steel said the company simply leased the lake to the angling club.

A Welsh fishery owner is trying to sue the Environment Agency for £2.5m for loss of stock after otters were reintroduced, in what would be a landmark case.