Pollution testing at pool over swan deaths riddle.
Environment Agency experts are analysing water samples from the Rattle Chain Mere pool, Tividale, after post-mortem examinations on the swans failed to establish the cause of their deaths.
Up to eight of the birds have died in the past three months at the lake, where chemical-manufacturer Rhodia has a licence to dump calcium phosphate waste.
John Scott, operations director for Rhodia, said calcium phosphate was not harmful to wildlife.
Results of the firm's own tests failed to establish what caused the death of the swans, he said, and the company was co-operating with the Environment Agency and liaising with the protection group Friends of Swan Watch while official investigations continued.
A spokesman for the Environment Agency said: 'Our officers have taken water samples and autopsies have been carried out on the swans but at this stage we are still unable to determine the cause of death.'