At present many of the fish are being eaten by seals

At present, salmon and sea trout are only able to negotiate the weir at Haverfordwest at high tide which means they are easy prey for predators.

The new pass is bad news for seals as they can regularly be seen feasting on the fish while they wait to swim up the Western Cleddau.

But anglers say the pass will be a boost to local tourism because when it is completed more fishermen will visit the area as there will be a better chance of getting a bite.

It will provide a massive boost to the local economy by attracting more visiting anglers Fisheries officer Ben Wilson

The pass, which is being built by the Environment Agency Wales, will allow fish to travel upstream at any time of the day.

The agency's fisheries manager in south west Wales, Ben Wilson, said the scheme incorporates the most modern technology on fish passes.

"No longer will the fish have to jump pool to pool but will be able to simply swim through the pass unimpeded," he said.

"It will not only benefit anglers, but will provide a massive boost to the local economy by attracting more visiting anglers.

Salmon will be able to pass the weir at any time of day

"This is part of a major investment in the sustainable development of fisheries in Wales."

Mark White who is chairman of the Pembrokeshire Anglers' Association said he was delighted the work had started.

"As an association, the improvement of the existing ineffective pass has been our main priority for a number of years.