Thames Water has been fined £2 million and ordered to pay full costs of nearly £80,000 after raw sewage polluted two Oxfordshire streams, killing almost 150 fish.

Judge Peter Ross, at Oxford Crown Court today (21 December) ruled that the incident in 2015 was a high-end category three harm offence.

The court heard that Thames Water ignored or did not fully investigate more than 1,000 alarms at one of its sewage pumping stations.

Thames Water was found to have been “reckless” in polluting Idbury Brook at Milton-under-Wychwood, near Chipping Norton, for up to 24 hours on 8 and 9 August 2015.

Numerous failures in the management of the Bruen Road sewage pumping station led to a backlog of raw sewage being forced into the water from a sewer pipe that could not hold it.

Sewage created by two villages emptied into two brooks leading to the River Evenlode, a tributary of the River Thames, for up to 24 hours.

Environment Agency officers discovered the entire local population of almost 150 bullhead fish had been killed by the toxic waste along a 50-metre stretch of water. Sewage also flooded a nearby garden.

Thames Water’s failure has been branded “reckless, foreseeable and avoidable” by the Environment Agency.

The court heard Thames Water disregarded more than 800 high-priority alarms needing attention within four hours, in the six weeks before the incident. Another 300 alarms were not properly investigated, all of which would have pointed out failures with the pumping station, the Environment Agency said.

One alarm was found to have been “deliberately deactivated” during a night shift.

Robert Davis, who led the investigation for the Environment Agency, said: “This incident was foreseeable and avoidable. Thames Water didn’t recognise the increased risk to the environment, ignoring or failing to respond adequately to more than 1,000 alarms.

“These streams are normally a haven for kingfishers, grey herons, brown trout and other fish and invertebrates.

“We hope this prosecution sends a loud and clear message that the Environment Agency will not accept poor operation, management and maintenance of sewage pumping stations. Where we have evidence of offending and serious pollution incidents like here, we will take appropriate action to bring polluters to justice.

“Judge Ross said Thames Water was ‘reckless’ by taking an unacceptable level of risk with the environment. It allowed the sewage pumping station to operate with no automatically available standby pump for around ten months in the year prior to the pollution.”

Environment Agency officers discovered other information and data highlighting repeated problems with the pumping station in the year before the pollution, which Thames Water failed to report to the organisation.

Thames Water pleaded guilty at an earlier hearing to two charges of breaching environmental law.

In a statement following the court ruling Richard Aylard, external affairs and sustainability director at Thames Water, said: “We take our role in protecting the environment extremely seriously and are really sorry for what happened here in 2015.

“We have made a series of improvements since this regrettable incident, including bringing in more people, more maintenance, more training and better systems. In the three-and-a half-years since, we have not had a serious incident at any of our 4,700 pumping stations.

“We would like to re-assure our customers that we continue to innovate and drive further improved performance right across the business, to help us achieve our ambition of zero pollutions.”

The Environment Agency said it expects Thames Water to ensure its 4,780 sewage pumping stations are maintained to a high standard to minimise the risk to the environment.