The River Thames turned bright blue and more than 2,000 fish died when chemicals leaked from a swimming pool, a court heard.

The Environment Agency told the court the 'category one' pollution incident was the worst they dealt with last year.

D C Leisure Management, of Surrey, which manages the Old Gaol Leisure Centre in Abingdon for the Vale of White Horse District Council, appeared at Didcot Magistrates' Court where it admitted polluting the Thames. The amount of chlorine in the water was 210,000 times greater than expected in a river.

On July 28, there was a leak from a tank of sodium hypochlorite used to treat water for the pool. Staff cleared up the spillage in the plant room but flushed it into the wrong sewer.

Vanessa Walker, for the Environment Agency, said: "It was not a reckless or deliberate act but one which could have been prevented had staff been aware of the drainage system and not assumed the drain used to discharge the chemical was a safe, foul sewer."

Peter Thompson, for D C Leisure, said it operated 80 sites and had not been prosecuted before. It was fined £7,000 and ordered to pay £4,100 costs.

But afterwards, Environment Agency protection officer Lisa Allen said she would like to see even bigger fines.