Thames Water’s event duration monitoring (EDM) map, which shows up-to-date storm overflow data for the water company's locations, reveals how long waste has been pumped into waterways amid stormy conditions over the past few days.

As of 11am today (January 3), Amersham Balancing Tanks/Amersham Vale has been discharging since 7.30pm on New Year’s Day (39 hours), Gerrards Cross Sewage Treatment Works has discharged from 2.45am on New Year’s Eve (80 hours), and Maple Lodge Sewage Treatment Works has not stopped since 8.45pm on New Year’s Day (38 hours).

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The same alert is currently displayed for each site, stating: “Our monitor indicates this storm overflow is currently discharging.

“This means there could be sewage in this section of the watercourse.”

Maple Lodge feeds into the River Colne while Gerrards Cross and Amersham both feed into the River Misbourne.

View the live map here

River Chess Association chairman Paul Jennings described the situation at the sites as a “travesty”, adding that his group has kept an eye on the “incredible” amount of sewage being pumped into nearby rivers.

The River Chess itself, a chalk stream, flows through Rickmansworth and faced sewage discharge from Chesham Sewage Treatment Works between 1.30pm and 10pm yesterday (January 2).

Although it has now stopped, Mr Jennings said it was “probably the largest we have had for some time” and a worse overflow than anything he can remember from 2023.

Combined with high levels of arable runoff due to rising water levels (which can carry fine sediment, pesticides, and fertiliser), discharge during storms can have potentially fatal consequences for wildlife particularly due to increasing ammonia levels.

Berkhamsted Sewage Treatment Works, which feeds into the Grand Union Canal discharged for 30 minutes between 9.30am and 10am this morning (January 3).

A Thames Water spokesperson said: “We regard all discharges as unacceptable and are sorry to those affected by this.

"We have published plans to upgrade over 250 of our sewage treatment works, including at our Maple Lodge and Gerrards Cross Sewage Treatment Works.

"The planned upgrades will improve our ability to treat the high volumes of incoming sewage and reduce the need for overflows during wet weather, as experienced across the UK in recent days.”

They also highlighted the impact of the storm and “exceptionally high” groundwater levels for the time of year.