River Thames has become an ‘open sewer' as treatment plants overwhelmed, report finds

People stand on the banks of the River Thames on a sunny day in London – a report has found the river has become an ‘open sewer’ – NEIL HALL/EPA-EFE/Shutterstock

The Thames is becoming an “open sewer” because treatment plants are overwhelmed, with more than half unable to cope with demand from local homes and business, analysis shows.

Of the 90 sewage works in the upper Thames, 46 don’t have enough capacity to deal with demand from local homes and businesses, a report has found.

The Oxford Rivers Improvement Campaign (ORIC) analysed data supplied by Thames Water to work out how much sewage its treatment works could process and whether it was enough to handle demand from local homes and businesses.

They said the data showed that the company’s failure to invest in upgrading its systems over recent decades was the cause of sewage leaks which has left the river polluted for wildlife, swimmers and rowers.

Thames Water is among water companies that have come under fire in recent months for dumping untreated sewage into rivers and the sea thousands of times.

It came as a video released by the BBC appeared to show sewage coming out of a pipe at Cassington sewage works, one of those covered by the study.

Video released by the BBC appears to show raw sewage coming out of a pipe at Cassington sewage works

ORIC data suggest Cassington has 74 per cent of the capacity it needs to process sewage correctly.

A spokesman for Thames Water said the plant had not released untreated sewage since March last year.

“Any problem seems to be occurring in the long pipe that takes the treated effluent to the river.

“We are determined to understand what is coming out of the final effluent pipe and we have taken further samples as part of our examination,” she said.

Not one of Britain’s rivers passes chemical pollution standards, and this week Britain’s only designated river swimming spot, in Ilkley, Yorkshire, was classified as “poor” after water quality tests showed it is heavily polluted with bacteria.

Some treatment not coping in normal weather

British sewage systems are designed to discharge untreated sewage into rivers and the sea when the volume becomes too great for them to process.

This is only supposed to happen at times of exceptionally heavy rainfall, but the analysis suggests that some of the treatment plants are also unable to cope with normal or dry weather.

The group’s analysis, seen by the Telegraph, shows that Oxford’s sewage treatment works had 61 per cent of the capacity it needs, while Swindon’s had 86 per cent and Banbury’s had just 43 per cent.

Mark Hull, a former water industry consultant and co-author of the report, said: “Our detailed modelling shows that half the sewage works in the upper Thames do not have enough capacity; they are not fit for purpose.

“We believe this is typical of the whole river Thames, and indeed many if not most rivers in England.

“Thames Water has taken customers’ money for treating our sewage, but not invested nearly enough to keep pace with the growth of housing.

“Our rivers have returned to being open sewers and sewage treatment works.”

A typical upper Thames sewage treatment works “discharges untreated sewage for around 500 hours a year”, the report says.

“The rises in demand were predicted twenty years ago and should have been taken into account in water companies’ investment plans for this century,” it adds.

‘Unprecedented’ amount of investment on solving issue

A spokesman for Thames Water said: “We regard all discharges of untreated sewage as unacceptable and will work with the Government, Ofwat and the Environment Agency to accelerate work to stop them being necessary.

“We have an unprecedented amount of investment directed towards safeguarding our rivers and streams.

“Between 2020 and 2025 we are spending £1.25 billion on maintaining and improving our operational sites, including contributing to the health of 745km of rivers across London and the Thames Valley.

“We’re increasing sewage treatment capacity at our sewage works in the area, including Oxford, Witney, Fairford and Ampney St Peter, and we’re also committed to continuing our industry-leading trial to provide real-time alerts of sewage discharges around Oxford in 2022.”