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  • Simon Collins

December pollution data is in!

Here are the pollution results for December 2023. Our fabulous River Mole River Watch citizen scientists collected data across the entire catchment.. here are the headlines: Compared with the peak pollution levels recorded in August (shown below), December phosphate levels are lower. In fact overall the December levels were some of the lowest we have recorded so far. The map above shows smaller blobs at each test site showing the lower phosphate levels compared with the large blobs below in August.

The lower readings are most likely due to dilution from higher river levels. The chart below shows the close correlation between phosphate levels and river discharge.

The December catchment average might be the "best"of 2023 but it is still only "Moderate" status on the Water Framework Directive scale. In December there were fewer streams of Good water quality but also the least tested as Bad. Usual polluted hot spots include Redhill Brook and Leigh Brook and 10 other sites recording Poor water quality status.

The running mean of our water quality tests in the River Mole catchment still shows that 87% of water bodies are in the Moderate, Poor or Bad quality.

Pollution levels are lower throughout the catchment. However, there are changes to the downstream patterns from the Summer with Winter phosphate levels lower in the Upper Mole but climbing a little in the Lower Mole. A hot spot at the Box Hill Stepping Stones shows a marked jump downstream of Dorking (Pixham) sewage treatment works.

Compared with other months, December pollution tests (blue bars on the right of each location on the chart below) show a marked fall in phosphate in the Upper Mole while pollution slightly increases downstream in the Lower Mole from Moderate at Norbury to Poor at Molesey.

Observations made by our testers included seeing a lot of fly tipping in places and foam over the Dorking weir at Castle Mill.

Finally, a sincere thank you to our valiant River Mole citizen scientists who tested between Christmas and New Year. They are expert car boot lab scientists!

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