Two billion litres of untreated sewage were dumped into the River Thames in just two days, a new report has revealed.

The equivalent of 800 Olympic-sized swimming pools in raw sewage was released from Mogden Sewage Treatment Works, in Isleworth, across 48 hours in October 2020.

These are just two of a series of spills linked to Mogden that have blighted local rivers and wildlife, alarming residents, local councillors and MPs.

The problems associated with Mogden, which is run by Thames Water, were included in a report published by MPs on the Commons Environmental Audit Committee (EAC) on the water quality of the UK's rivers.

According to the report, Mogden, the UK's third largest sewage treatment works, poured one billion litres of contaminated water into the Thames on October 3 and the same amount was dumped on October 4, 2020.

In the whole of 2020, 3.5 billion litres of untreated sewage was poured into the Thames by Mogden.

This was an increase of 600 per cent from 2016 when Mogden spilled 0.5 billion litres of sewage into the river.

Nub News revealed last year, how Thames Water was condemned for delays in cleaning up a devastating storm water sewage spill from Mogden into the Duke of Northumberland's River and on to the Thames.

The fragile river environment was littered with plastic bags and other waste some three weeks after the incident.

At a recent Richmond council meeting, a motion, moved by Councillor Julia Neden-Watts and seconded by Councillor Lotte Campanale, was passed to highlight the damage that releases of untreated sewage cause.

Councillors stressed that the discharges are also a threat to human health given the fact that wild swimming, kayaking and paddle boarding are becoming increasingly popular.

The Twickenham MP, Munira Wilson, recently raised her concerns about Mogden on a visit to the plant, which receives sewage from 2.17m people across west London.

The site treats 12,314 litres of sewage per second but will need to invest £100m over the next three years to support population growth.

The MP said: "Discharge into the river should be an extremely rare occurrence and I urged Thames Water to do everything in their power to reduce the number and scale of these incidents."

The Thames Water chief executive, Sarah Bentley, said that problems in October 2020 involved two of the wettest days on record.

Mogden's eight storm tanks were unable to cope with the volume of rain, causing sewage to be dumped into the Thames.

Ms Bentley said: "We would have needed either another treatment works the same size as Mogden treating another 1 billion litres or we would have needed 150 more storm tanks (to cope with the rainfall)."

Sewage overflows are legal when sewers are likely to become overwhelmed.

Releasing the sewage into rivers prevents it from backing up into homes and spilling out of toilets and bath plugholes.

Residents living close to Mogden Sewage Treatment Works have complained about the works for several years.

Councillor Salman Shaheen, who represents the ward of Isleworth for Hounslow Council, said residents were furious to read the report's findings and called on Thames Water to do more to help Mogden's deal with increasing sewage.

Cllr Shaheen said: "People are very angry. They are outraged to hear about it because their kids are paddling in the Thames.

"It really is a treasured resource we have in our part of West London and it is being polluted by a water company.

"Mogden needs to upgrade their facilities. They must increase its storm tank capacity to prevent spillages into the Thames. It can't be allowed to continue at this level."

Labour MP for Brentford and Isleworth Ruth Cadbury said: "I've supported residents in their campaigns for urgent and sustained action, including calling for Thames Water to expand their capacity and address the crisis of sewage and flood water overwhelming the Mogden and their other sewage treatment works.

"Only then can they reduce the need to pump sewage into the Thames."

A spokesperson for Thames Water said: "We welcome the findings of the EAC report which brings the collective issues affecting England's rivers to the fore.

"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.

"We continue to upgrade Mogden sewage works to help meet growing demand and we have £22 million of investment planned to improve the site's performance and power generation capabilities.

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