Thames Water has been ordered to pay £15,000 after a raw sewage leak killed hundreds of fish.

Untreated sewage flowed into Emma’s Dyke, in Witney, killing about 650 fish in December 2007.

Thames Water pleaded guilty at Banbury Magistrates’ Court to two charges under the Water Resources Act.

The firm was fined £10,000 and ordered to pay £5,074 prosecution costs.

The court heard on November 30, 2007, a member of public tipped off Thames Water sewage had leaked into the waterway but since stopped.

Thames Water notified Environment Agency but cancelled a planned visit to check if the water was polluted.

A week later a member of the public raised the alarm to the Environment Agency.

Experts discovered Emma’s Dyke has turned a milky colour and estimated 50 dead fish at the scene of the sewage leak.

Samples later revealed high levels of ammonia and other pollutants and 650 fish – half of all fish in the Dyke - were found dead over a 300m stretch of the waterway.

The sewage leak was classified by the Environment Agency as the most serious of its type.

Environment Officer Emilie Vonck said: “Thames Water made a serious error in cancelling its contractors from attending the incident on the 30 November 2007.

“Water companies have a statutory duty to maintain their sewers, which Thames Water had not done in this case. It sends a clear message to other companies that if you fail in your environmental responsibilities you may be prosecuted".

It is estimated it will take three years before the waterway is back to normal with a healthy fish population.

Members of the public are encouraged to contact the Environment Agency on-0800 807060 where they have observed signs of a pollution incident at any of their local watercourses.