The summer drought has exposed alarming new pollution hotspots, striking differences between tributaries, and an intriguing discovery: the Upper Mole's lowest summer flows appear to have risen by 30% over recent decades. September brought continued exceptionally low flows across the River Mole, including here at the popular Stepping Stones — a beautiful river scene, but one that hides growing concerns about drought and water quality. Our September citizen science testing reve

Summer 2026 Record heat, vanishing flows and late-summer rain exposed new nutrient hotspots across the River Mole catchment. Summer 2026 gave the River Mole an exceptional stress test : record heat, no rainfall in the catchment during July, extremely low flows and the river itself vanishing through the Mole Gap. Our monitoring revealed several important changes. Treated sewage effluent became visibly important to the river’s flow. Daily “wastewater tides” could be traced thro

July’s water-quality testing took place in exceptional dry-weather conditions at the end of July, with the River Mole already under severe low-flow stress. This is a short summary of results. Zero rainfall in July. Cattle at Swanworth Farm in the Mole Gap (pic courtesy Nick B, the farmer) By the July test weekend there had been 0 mm of rainfall for the month to date, no storm overflows had been recorded in the catchment, and River Mole flow at Leatherhead had fallen to just 0

River Mole River Watch has submitted our evidence into two important planning processes that went "live" recently: the Environment Agency’s Programme of Measures (PoM) and Thames Water’s Drainage Wastewater Management Plan (DWMP28). Together, these plans should show whether evidence from local groups who know the catchment is being used to shape real action for the River Mole. River Mole River Watch met with Environment Agency catchment officers this week, alongside other mem

Site visits supporting our Reading University PhD student embarking on a study of the River Mole River Mole River Watch’s June 2026 citizen science test results show a catchment under serious stress from different causes. Our regular testing took place over the weekend of 27-28 June after a hot, dry two weeks, with low river flows, high water temperatures and very little dilution. Following the second heatwave of the year, our phosphate data show serious pollution pressure wo

May 2026: a dry spring increases pollution pressure May 2026 completed a mostly dry, low-flow spring across the River Mole catchment. Our latest citizen science results shows pollution pressure quickly rising as rainfall fails, river flow drops and water temperatures rise. Given we are entering the second heatwave of the year already, this provides us a window into how the river might change in a warmer world. May snapshot The catchment average phosphate rose significantly fr

What our ammonia, nitrate and phosphate tests tell us about pollution Rivers need nutrients, but only in the right amounts. Nitrogen, phosphorus and ammonia occur naturally in soils, plants, animals, decaying leaves and animal waste. They are also found in fertilisers, sewage, treated effluent, road and farm runoff. Problems start when too much nutrient pollution reaches the river, especially during warm, low-flow conditions but also during prolonged storm overflows. Excess n

April was an exceptionally dry month across the River Mole catchment. With only around 5 mm of rain recorded before testing, river levels fell and pollution concentration strengthened. This month’s citizen science results show what often happens as the catchment moves from winter into spring: nutrient concentrations begin to rise, some streams remain in good condition, while others, including those shown below, showed a significant increase in pollution pressure. See foot of

March brought a marked spring shift in River Mole catchment water quality. Across our 33 monitoring sites, phosphate, nitrate and conductivity all rose noticeably compared with February as less rainfall fell, river flows dropped and dilution decreased. This month we review those changing seasonal conditions, examine the main pollution hotspots emerging in the River Mole and tributaries, and compare the latest storm overflow data with recent years to assess whether progress is

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...