Thames Water has been fined £10,000 and ordered to pay costs of £4,488 for polluting Faringdon Stream in Faringdon, Oxfordshire between 14 and 16 August 2011.
The company was also ordered to pay a victim surcharge of £15 at the hearing at Oxford Magistrates Court on Friday.
The court heard how a breach in a Thames Water sewage inlet pipe downstream of Faringdon Sewage Treatment Works caused sewage to overflow and discharge into an area of woodland and flow into Faringdon Stream. The discharge lasted for more than 48 hours and caused a significant deterioration in water quality and the invertebrate community.
Environment Agency officers visited the site on the 17 August and noted dead fish, including chub, dace, perch and roach which appeared to have been dead for some time. Water quality samples were taken to check levels of ammonia, suspended solids and oxygen. The measurements indicated sewage pollution at levels consistent with the death of the fish. It is estimated that upwards of 270 fish were killed by the sewage pollution in total.
During the investigation Environment Agency officers found that there had been a burst on another part of the same pipe in the close vicinity in September 2003. There was no further investigation at that time which Thames Water told the court is in accordance with standard industry practice. The pipe was installed prior to 1974 but Thames Water has said that it is rare for gravity sewers to collapse and that each pipe failure is assessed independently to see if replacement is required.
Thames Water has made a decision to replace a short section of pipe but these works have not yet been carried out.
Jack Knight, the investigating Environment Agency officer, said:
“Rivers and water courses are an important part of the environment; they offer an essential resource for wildlife, fisheries and recreation. It is distressing when incidents such as this one occur and cause fairly significant environmental damage, with several hundred fish killed by this sewage spill.
“The prosecution and fining of Thames Water sends a clear message to other companies that if you fail in your environmental responsibilities you may be prosecuted.