A water utility in the southeast of England has been fined after allowing partially treated sewage and an illegal storm discharge to enter a local river.

Thames Water will have to pay a fine of £220,000 ($340,000) and costs of £27,500 ($42,500) for the pollution in the River Blackwater, which killed a significant number of fish, including roach, gudgeon, minnow, perch, dace and chub.

In a hearing at Guildford Crown Court the water company pleaded guilty to breaching its environmental permit and causing pollution to an environmentally sensitive site on September 7 and 30, 2012, when illegal discharges of effluent occurred from its sewage treatment works in Camberley.

According to the Environment Agency, which brought the case, the problem at the sewage works led to partially treated effluent being discharged into the river. This had the effect of suffocating fish by depriving them of oxygen over a mile-long stretch of the river.

Thames Water blamed the problem on its contractors, but Judge Lucas QC ruled that the company had been reckless in relation to the incident and that significant environmental harm had been caused.

Andrew Valantine, senior Environment Agency officer, commented: "Unfortunately this was a serious incident which led to fish being killed and the water quality being badly affected over a significant stretch of the river. Our team responded immediately by using aeration units to quickly pump much-needed oxygen back into the river and reduce any further impact from the sewage works."

Judge Lucas QC concluded: "It is important that the courts send out a clear message to Thames Water and all companies operating in this sector. Regulations are there to protect the environment and that the courts will act firmly where regulations are breached and where the environment is either damaged or put at risk of damage."