So far 32 swans have survived the pollution

So far 32 swans have survived, but a number of moor-hens and ducks have died after the leakage into the River Soar in Leicester over the weekend.

Staff at Leicestershire Wildlife Hospital have worked around the clock since Saturday morning cleaning affected birds.

"We're extremely angry with what's happened. But obviously the main priority now is to try and rescue as many birds as possible", said hospital volunteer Sophie Carter.

We suspect somebody's opened up a man-hole and tipped probably around 500 gallons of waste oil into the sewage system Steve Proffitt, Environment Agency

The oil can poison them if they swallow it in trying to peck it off.

It also it stops their feathers being waterproof, leading to death from pneumonia.

Meanwhile the Environment Agency says heavy rain has hampered the clean-up operation.

The Environmental Agency believes the oil was dumped on purpose

Spokesman Steve Proffitt said the oil leaked from a pipe between Filbert Street and the New Walkers Stadium.

"We suspect it's been dumped. We suspect somebody's opened up a man-hole and tipped probably around 500 gallons of waste oil into the sewage system.

"Someone's trying to avoid paying the costs of disposing of it."

He appealed for witnesses who may have seen anything suspicious on Friday afternoon.