Thames Water dumped sewage for more than 68,000 hours into the river systems around Oxford last year, campaigners have revealed.

Oxford Rivers Improvement Campaign (ORIC) analysed the Environment Agency’s data on sewage discharges for 2021 and its database of investments by water companies.

Across the upper Thames, 102 sewage treatment works discharged into the rivers in 2021. Forty-nine discharged for more than 10 hours a week and almost quarter of the works discharged for more than 1,000 hours in the year.

The water company discharged raw sewage into the Thames and its tributaries including the River Windrush, Thame, Evenlode and Ock 5,028 times that year, according to the data.

And the latest report from ORIC reveals that, according to the EA investment database, only a third of the Upper Thames works which need investment will be upgraded by 2025.

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That figure falls to a quarter when the region's rising populations are taken into account.

Using data from Thames Water and applying the Environment Agency formula for capacity required at any treatment works, the campaigners assessed that the 10 large sewage treatment works in the upper Thames area – from Didcot in the south to Moreton-in-Marsh and Bourton-on-the-Water in the Cotswolds – were unable to treat the full capacity of sewage for the population of 1.1 million.

Their calculations indicate Oxford and Witney treatment works can cope with only 62 per cent of the capacity needed for the population, and the treatment works in Banbury for 49 per cent of the required capacity.

All 10 works discharged sewage into the rivers in 2021 for an average of 11 hours a week.

Oxford sewage treatment works released raw sewage into the waters for 892 hours in 2021, Swindon for 501 hours and Witney for 935 hours.

The report, published on Wednesday by ORIC, found that even where Thames Water had planned investment, the expansion of capacity would not be sufficient to meet the growing number of homes.

At Witney treatment works the investment will increase capacity by 50 per cent but that would improve the works to only 93 per cent of the required capacity based on the 2020 population, the report says.

"The simple truth is that Thames Water's plans are completely inadequate," said ORIC's Mark Hull, a former water industry consultant.

"Given the well-established and long-standing problems faced across the Upper Thames region, it is scandalous that appropriate and coordinated investment plans for the whole region are not in place.

"Thames Water and the Government's Environment Agency have both failed to deal with this problem over many years. Their ongoing under-performance beggars belief - especially as the industry's financial regulator OFWAT have made it clear that they would not oppose the necessary investment.

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"Two urgent questions need to be answered. How has this been allowed to happen? And what do we do about it?

"Government, the Environment Agency and Thames Water keep telling us that they are dealing with the problems. The truth is simple. They are not."

A spokesperson for Thames Water said it was examining the ORIC report.

“Our aim will always be to try and do the right thing for our rivers and for the communities who love and value them. 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 and are determined to be transparent.

“We recently launched our river health commitments, which include a 50 per cent reduction in the total annual duration of spills across London and the Thames Valley by 2030, and within that an 80 per cent reduction in sensitive catchments.

"We have a long way to go – and we certainly can’t do it on our own – but the ambition is clear.”