River Mole River Watch citizen science reveals how storm overflows pushed pollution higher during the season rivers should have lowest pollution concentration. This winter our dedicated citizen scientists have been out testing in rain and flood conditions, and their data are now revealing a clearer and more detailed understanding of how the River Mole behaves during winter high flows and prolonged periods of sewage overflow activity. Within this growing dataset, some concerni

A Newsflash prompted by recent observations and monitoring results, issued ahead of our next scheduled February catchment update coming soon. More than one kilometre of Earlswood Brook is currently coated in extensive sewage fungus downstream of Reigate / Earlswood Sewage Treatment Works (STW), following a period of prolonged storm overflow activity at the site. The growth blankets large sections of the stream bed, banks and in-channel debris in thick grey-brown mats — a well

Flooded River Mole at Cobham Our fantastic team of citizen science volunteers were out again monitoring the health of every river and stream in the Mole catchment on 24-25 January following flooding which peaked on 22 January. Their tests revealed something genuinely new in our water quality data. Despite very high river levels and the dilution that usually comes with them, we recorded unusually high ammonia and phosphate concentrations , particularly in small tributaries do

Here's a quick round-up of the recent flooding on the River Mole (20–24 January) Between 20 and 22 January , around 40 mm of rain  fell across the River Mole catchment. That total isn’t remarkable on its own — but the way the rain arrived made this flood more interesting than a simple one-off downpour. (No photos here... please see our Facebook page for observations from our members of this flood event.) Instead of falling all at once, the rain came in several distinct burst

Happy New Year and Happy New Charts! December’s River Mole River Watch water quality monitoring took place in unusually high flow conditions after a storm dropped over 35mm of rain a few days prior to the test weekend. The rain triggered widespread storm overflows across the Thames Water assets in the catchment, resulting in prolonged discharges of untreated sewage which was transported downstream. Data from December tests can potentially show how the river responds to recen

Autumn water quality provides a revealing window into the health of the River Mole.  As the river transitions from summer low-flow conditions toward winter recharge, the catchment’s sensitivity to rainfall, geology and pollution sources becomes especially apparent. At a glance, November headlines show the river in poor condition despite the dilution effects of higher river levels, a considerable decline in storm overflow duration and evidence of effective phosphate treatment

Here’s our October round-up from River Mole River Watch citizen-science testing across the River Mole and a dip into exciting data from the new AquaWatch live "Waka" sensors installed in September. October’s long dry spell finally broke with some substantial rain in the days just before our test weekend. This brought a welcome fall in phosphate, nitrate and ammonia levels after very high concentrations were measured during the dry spell with low flow in September and early Oc

We're changing our water quality reporting format to include a shorter snapshot report each month with a more detailed quarterly seasonal...

Summer 2025 put the River Mole under real pressure. Following the driest spring in over a century, June and August brought parched conditions and record heatwave days. Normally this would mean rising pollution and stressed aquatic life — but a very wet July, with nearly double the usual rainfall, diluted the river just enough to avert a crisis. Our citizen science monitoring shows this was a near-miss. Phosphate levels dipped slightly compared with 2024, but more than 70% of

This month, we're highlighting the parlous state of one small stream in our catchment: Hookwood Common Brook draining into the Mole to...

This month's water quality reports is a more concise summary. We plan to do a comprehensive seasonal analysis at the end of the summer...

Where Did the River Go? Understanding the Vanishing River Mole Every so often—perhaps once in a generation—the River Mole performs a...

Welcome to a round-up of news and the latest river data from River Mole River Watch. Mapping swallow holes in the Mole Gap with Nick the...

League Table of Most Polluted Water Courses *built from weighted data In the Spring of 2023, our citizen scientists began monthly data...