Thames Water could be fined over £100 million for failing to manage its wastewater treatment works.

Regulator Ofwat has today (6 August) proposed three water companies will be fined a total of £168 million, as part of the first batch of outcomes from its biggest ever investigation.

Alongside £104 million for Thames Water, Yorkshire Water may have to pay £47 million and Northumbrian Water a further £17 million.

The penalties relate to their management of wastewater treatment works and wider sewer networks including their operation of storm overflows.

These are designed to release water in exceptional circumstances, when the sewerage system is at risk of being overwhelmed, such as during unusually heavy downpours or snowfall, to prevent sewage flooding into people's homes.

In addition to the proposed financial penalties, Ofwat is also consulting on proposed enforcement orders which will require each company to rectify the problems identified.

Ofwat is able to fine companies up to 10 per cent of their annual sales.

Companies will not be able to recover the money for any proposed penalties from customers and "Ofwat will ensure that customers are not charged twice" where additional maintenance is required.

Ofwat's chief executive David Black said: "Ofwat has uncovered a catalogue of failure by Thames Water, Yorkshire Water and Northumbrian Water in how they ran their sewage works and this resulted in excessive spills from storm overflows.

"Our investigation has shown how they routinely released sewage into our rivers and seas, rather than ensuring that this only happens in exceptional circumstances as the law intends.

"The level of penalties we intend to impose signals both the severity of the failings and our determination to take action to ensure water companies do more to deliver cleaner rivers and seas.

"These companies need to move at pace to put things right and meet their obligations to protect customers and the environment. They also need to transform how they look after the environment and to focus on doing better in the future.

"Looking to the future we want transform companies' performance under our new price control that starts in April next year, so we reduce spills from sewage overflows by 44 per cent by 2030 compared to 2021 levels."

Liberal Democrat MP for Richmond Park Sarah Olney said: "For years under the last Conservative Government, Thames Water was allowed to get away with polluting our rivers with filthy sewage.

"It is therefore welcome to see they are finally being held to account for their actions. 

"However, this should just be the start.

"We now need a ban on bonuses and an end to huge profits for polluting water companies - forcing them to clean up their act and end this sewage crisis for good."