Thames Water has announced plans to spend a record £1.6billion over the next two years on upgrading sewage treatment works and sewers.
This is more than double its investment in sewage related infrastructure in the previous two years.
But chief executive Sarah Bentley admitted levels of pollution in rivers today were the result of “decades of underinvestment”.
And Cotswold campaigners blasted it as a public relations exercise.
One of the key projects is £15million to expand and upgrade Witney Sewage Treatment Works, which currently serves 45,000 people, to reduce the number of storm discharge incidents.
Last month Thames Water's interactive map of storm overflow spills showed that Hardwick Brook in the Rushy Common Nature Reserve near Witney had almost four days of sewage dumped into it over a week in January, making it the worst in the Thames Water region.
READ AGAIN: Sewage released in West Oxfordshire continuously for 20-plus days
The spills came despite only 3mm of rain over the period.
A storm overflow at Standlake discharged 122 hours of raw sewage into the River Windrush on New Year’s Eve.
Announcing the funding Ms Bentley said: “The discharge of untreated sewage is unacceptable, and we are committed to tackling this problem.
"We are investing record sums in upgrading our sewer systems and treatment works and are striving every day to reduce the discharge of untreated sewage into our rivers.
“However, there are no quick fixes. Population growth will increase the strain on our sewage network and treatment centres.
"And because of climate change, the south east of England is experiencing heavier downpours, which can overwhelm some sewage treatment works.
"The scale of the challenge demands urgent and systemic reform with a shared undertaking from all stakeholders.”
Thames Water says the upgrade at Witney will provide a major increase in treatment capacity, from 240 to 399 litres per second – a 60 per cent increase in capacity.
It says this will reduce the need for untreated discharges in wet weather.
The work is running ahead of schedule and is currently expected to be complete early in 2024.
But environmental campaigners Windrush Against Sewage Pollution blasted the announcement.
They said it had taken three years of 'direct engagement with the CEO, a relentless media barrage and a creditable effort from the Environment Agency to force Thames Water to a long overdue upgrade' at Witney.
Chair Ash Smith said: "Last year councillors joined WASP for a water company briefing where the planned work was explained alongside a cost of £8.8million.
"That has now gone up to an eye-watering £15million for what we believe to be the same outcome.
"So the question we are asking is why, and what do the people of Witney actually get for that money - because it will be the Thames Water billpayers who fund it, not the shareholders."
He added that "water companies are still polluting and failing massively but are agitated and now pushing public relations very hard to reclaim credibility against a backdrop of hard-evidenced criticism from campaigners."
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