Sewage discharged into River Mole for hundreds of hours over five days
Sewage was pumped into the River Mole for nearly 800 cumulative hours over a five-day period in January, according to figures released by Thames Water.
Last updated 4th Feb 2026
Members of the River Mole River Watch in Surrey said the discharges took place between 20 and 24 January, during a period of heavy rainfall in the days leading up to Storm Chandra.
The group said the scale and duration of the discharges had caused serious harm to the river. Trustee Simon Collins said: “When this happens, the whole river suffers.”
"So what's happened to the mole over the last few weeks and months, really is that January has been an extremely wet month. It's the third wettest on record in the southeast, and it wasn't extreme rainfall at any stage, but it was just rain fell very frequently."
"The biggest event we had was 35 to 40 millimetres."
"Now you'd normally expect pollutants to be diluted by high amounts of river water, but in this case, it was quite different, and our data showed some very unusual, unusual pollutants in the water course."
High bacteria levels recorded
The campaign group said water testing at Fetcham Splash recorded E-coli levels of more than 10,000 colony forming units per 100 millilitres - more than ten times the legally safe limit of 900.
Collins said that while large storms would normally dilute some pollutants, that did not happen in this case.
“Levels actually rose because of the enormous length of time that some of these overflows were discharging into the river,” he said.
What are cumulative sewage discharges?
Cumulative hours are calculated by adding together the total time that multiple sewage overflows are active during a set period.
Sewage overflows are designed to operate when heavy rainfall overwhelms sewer systems, allowing excess sewage to be released into rivers to prevent it backing up into homes.
Political reaction
Dorking and Horley MP Chris Coghlan said he had written to Thames Water, describing the discharges into the River Mole as “unacceptable”.
Thames Water response
Thames Water said it was investing heavily in its wastewater infrastructure.
A spokesperson said: “We are delivering record levels of investment across our wastewater infrastructure and are committed to seeing waterways thrive.
“But we can’t do it alone. Farming, industry, road runoff, wildlife, and increasingly extreme weather also play a role in river health.”
The company added: “We understand that all untreated discharges, even when permitted, are unacceptable. However, it’s important to remember the sewage system was historically designed this way to prevent sewage backing up into people’s homes.”
What you can do
Collins told us how locals can get involved to protect the river:
"Local residents can help by supporting groups like ours."
"Most river catchments have groups like river mole, river watch, and we work really hard. We're all trained, we're all unpaid volunteers, and we work really hard to try and do what we can to improve the river for people and wildlife."
"So if people want to do something for the local river, remember this."
"These are corridors of of important habitat which connect up nature reserves and areas of outstanding natural beauty, like the North downs, they flow through this, so they're extremely important areas for wildlife and also for the enjoyment of people as well."