Sewage discharges could last months after waste was pumped into the River Chess non-stop for 800 hours in March, a river association has warned.

The Chesham treatment works started discharging overflow water at 6.45am on February 29 and is still ongoing, according to a live map run by Thames Water 

River Chess Association chair Paul Jennings said Thames Water, which owns the treatment works, had failed to stop groundwater from entering the sewage system and overloading the facility.

Thames Water has previously admitted that the Chesham treatment plant had “a history of prolonged storm discharges”, and is currently carrying out £20 million improvement works at the facility.

Watford Observer: The Chesham sewage treatment works has been releasing untreated water for the whole of March.The Chesham sewage treatment works has been releasing untreated water for the whole of March. (Image: Thames Water)

The water company said it has increased its capacity by 40 per cent, lined 144 metres of sewers, and sealed 256 manholes to prevent surface water getting into the system.

But Mr Jennings warned: “The increased capacity is certainly not enough to deal with what we're having to deal with at the moment. You would need to probably see about a 200 per cent capacity increase for it to even come close. 

“Unfortunately, there doesn't seem to be any respite in sight to be honest. This could go on for another month or two.”

A Thames Water spokesperson said: “We regard all discharges as unacceptable and we have published plans to upgrade over 250 of our sewage treatment works, including at our Chesham Sewage Treatment Works."    

The updates worth £20 million will allow it to treat sewage at 353 litres per second and reduce the need for discharges in wet weather, the spokesperson claimed.

They also said the outflows protected people’s homes by releasing wastewater before the sewer system is overwhelmed.

Thames Water maintains that improving the health of rivers was a “key focus” and that it was the only company to provide live alerts for sewage discharges.

It comes after data recently revealed that the amount of raw sewage spills into England rivers and seas doubled in 2023. There were 3.6 million hours of spills compared to 1.75 million hours in 2022, according to the Environment Agency.

It showed that on average, there were 1,271 sewage discharges a day across England, compared to 825 in 2022.