Is pollution behind the deaths of millions of cockles worth £7m?

Local cockle pickers say that pollution from a nearby sewage works is to blame, although water company chiefs dispute the claim.

About 6,000 tons of cockles, worth £7million, were wiped out at the Burry Inlet cockle bed off the Gower Peninsula, South Wales.

Livelihood: Cockle pickers in Gower, South Wales, have found 6,000 tonnes of dead shellfish

Pollution in the water could have caused the deaths by weakening the immune system of the cockles, said one expert, Dr Ruth Callaway from Swansea University, adding that parasites or disease could also have been to blame.

'But pollution would most likely affect several species and not just the cockles,' she added. 'We've looked into the usual suspects but there is no clear lead on what the reason could be.'

A spokesman for Welsh Water said the firm had been told by experts that the cause was complex, involving several factors. The company warned against 'jumping to conclusions'.

Experts are baffled at the cause - and scale - of the deaths, which are threatening the future of the local shellfish industry.

It's the latest marine massacre in a grim few months for Britain's sea creatures.

Mystery: A dead cockle from the beds of the Burry Inlet near Llanelli

Earlier this week, 26 dolphins were killed after becoming stranded in shallow waters near Falmouth, Cornwall.

And in March millions of starfish were washed ashore in Kent and Sussex after one of the biggest strandings in years.

The Burry Inlet cockle bed is one the most productive in the UK. More than 50 cockle pickers earn their backbreaking living raking shellfish from the sand.

But in recent weeks, the number of dead cockles found buried in the sand has been growing.

The fishing community now fear their industry is at risk if something isn't done to stop polluting of the seabeds.

Cockler Glyn Hyndham said: 'It's a disgrace that all these cockles have been killed. I believe it is down to water quality and pollution.'

Tasty treat: Cockles ready to sample on a stall at Swansea Market

Some cockle pickers have openly accused Welsh Water. The company said it had invested around £50 million in the last decade on improvements to the sewer network in the area and that there was no evidence it was to blame.

Cockle-picking boss Mark Swistun dismissed theories of pollution or a mysterious disease. He believes cockles are victims of their own success.

'The problem is that the juvenile cockles are so healthy they are spawning at a massive rate which weakens them,' said Mr Swistun managing director of Penclawdd Shellfish Processing.

'That leaves a large majority not strong enough to survive.'

Thousands of dead cockle carcasses on the huge underwater mud flats off the Gower coast then rot and infect healthy cockles which have survived.

'It used to be that every three to five years we would have a bumper crop but in the last five or six years every year has been a bumper crop, and better than the previous year,' he said.

'The cockles are so healthy in my opinion they are their own worst enemies.'