Sewage has been discharging into the River Chess for over 400 hours, with no sign of stopping yet.

Sewage has been discharged from The Chesham Sewage Treatment Works into the River Chess since 6:45am on February 29, totalling nearly 500 hours of pumping, according to Thames Water’s Event Duration Monitoring (EDM) map.

Paul Jennings, chair of the River Chess Association, said many residents have “complained of bad smells” in the area, with the river’s water quality “getting worse day by day”.

The association had been working closely with Thames Water to increase the capacity of the Chesham Sewage Treatment Works prior to last month –"positive work" that Paul said has been negated by the ongoing situation.

“What we need is a firm plan for resolving the problem of sewage discharges. We thought we had that in our work over the last three years, but we obviously haven't managed to solve the problem."

He also expressed concern about the impact the discharge would have on wildlife in the area – including water voles, river trout and otters that had returned to the Chess after 50 years in 2019.

The magnitude of the discharge is due to the Chesham plant being impacted by high groundwater levels as a result of recent rainfall, filling up its storm tank and discharging untreated flows into the river to a near-unprecedented degree.

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In a statement addressed to the association on March 11, Thames Water acknowledged that the discharge was “causing considerable anxiety” to residents, especially after the treatment works broke its boundaries and flooded Blackwell Hall Lane at the beginning of the month.

A spokesperson said: “The Chesham Sewage Treatment Works has a history of prolonged storm discharges into the River Chess, so over the past four years, we have been investing heavily in both the sewage system in the Chesham area and the treatment works by 40 per cent. The site can now treat at least 353 litres per second of wastewater before we need to use the storm tank.

“None of this excuses the fact that storm discharges were made, but we are clear that, without the improvements delivered to date, discharges would have started earlier and been more prolonged than we are currently seeing.

“After so much rainfall, we are now in a period where groundwater is likely to continue to rise, regardless of the weather. We expect this to put continued pressure on our ability to treat all incoming flows and as a result, anticipate the discharges will continue for the immediate future. We are continuing to monitor the catchment to enable us to further understand the challenges and plan improvements for further years.

“I apologise that we are unable to prevent these discharges and assure you that we remain committed to delivering the further improvements necessary to protect the River Chess and its environment.”