They say there's no obvious reason why 6,000 tonnes of the shellfish off Gower have died.
Some people think it's because the water is polluted, but although scientists say it's possible, they think there could be other reasons. One scientist, Matt Longshaw, said some infections had been found in the dead cockles, but none of them were harmful to humans.
Dr Ruth Callaway from Swansea University said it was possible the cockles were being affected by pollution.