THAMES Water allowed raw sewage to leak into the River Windrush and three other watercourses, a court heard.

The company was fined £100,000 at Witney Magistrates Court yesterday, after admitting allowing the sewage to pollute the River Windrush, Colwell brook, Curbridge ditch and Emmas Dyke in February 2004, in breach of the Water Resources Act 1991.

It also admitted six charges of breaching its consent to discharge storm sewage from Witney sewage treatment works on six separate occasions.

The company was fined £7,000 for each of the six charges of breaching discharge consents, and £8,000 for polluting the four watercourses. It was also ordered to pay £25,000 in costs.

An Environment Agency spokesman said that in the event of heavy rainfall, when sewage works may receive more sewage than it can deal with, excess was stored in storm tanks to be dealt with later; however, in the event of prolonged rain and when the storm tanks were full, the works was allowed to discharge straight into the rivers.

However, due to an incorrectly set weir at the Witney works, the storm tanks filled quicker than they should have, and sewage was discharged into the river when it should not have been.

Senior environment officer at the EA, Stephen Wilkes, said: "Thames Water's failure to ensure that its storm sewage weir settings were correct meant that four watercourses were seriously affected by sewage fungus. We believe that the weir level was set incorrectly for a long time, causing unnecessary and unacceptable pollution.

"These intermittent discharges caused chronic pollution and had a serious impact on the water quality and ecology of the watercourses.

"Storm sewage discharges are infrequent and when they occur, the amount of rainwater should dilute the untreated water sufficiently to reduce any impact on the environment.

"But in this case, any impact was magnified because storm discharges occurred more frequently, for longer periods and with a stronger effluent than intended and described in the consent, due to the incorrect weir level."

The court heard that due to the incorrect weir setting, the site was only running at three quarters of its capacity for an unknown time, possibly years.

The Environment Agency began its investigation on February 13, 2004, when a member of the public reported sewage being discharged from the sewage works even though there had been no rainfall.

Environment officers found stretches of Curbridge ditch, Colwell Brook and Emma's Dyke were badly polluted with grey sewage fungus across the bed of the streams.

Thames Water admitted that the weir level had been set incorrectly.

During the case the district judge Brian Loosley said that the company was at fault for failing to check and rectify its error much sooner.