Twenty citizen scientists were involved in a monitoring programme, testing water quality on a stretch of the River Thames running from South Stoke to Pangbourne. They wanted to find out how effectively effluent is treated at local sewage works. Here’s what they found.
The testing protocol and results
The citizen scientists were trained in water quality sampling, employing a protocol developed by TH Environmental Ltd for The Rivers Trust which follows practices required by the Bathing Water Directive 2006/7/ec.
The 2024 bathing water season in this region was characterised by dry, warm weather, until a period of heavy rainfall in September, with less extreme heat as seen in previous summers. Results in this programme were predominantly ‘Good’ at every sample point, except Sulham Brook which saw higher levels of IE, bringing its overall designation down to ‘Poor’. The heavy rainfall seen in late September would likely be labelled an ‘abnormal situation’ by the Environment Agency (EA) under its bathing water monitoring methodology, and thus disregarded[1].
Citizen scientists monitored at six sites. Using the EA water monitoring classification, here were the results for each site:
Sample point A: EC Good IE Good
Sample point B: EC Good IE Good
Sample point C: EC Good IE Good
Sample point D: EC Good IE Excellent
Sample point E: EC Good IE Good
Sample point F: EC Good IE Poor
What the results mean
The results of this monitoring programme indicate that the sewage treatment works (STWs) upstream of Pangbourne are functioning effectively during dry weather, and only extreme levels of rainfall will cause negative impacts to water quality. One positive conclusion of this programme’s results is that the higher Faecal Indicator Organism (FIO) counts seen upstream at Wallingford during earlier stages of the bathing season appeared to have reduced by the time the Thames reaches South Stoke. This points towards the contained impact of bacterial pollution on water quality and the self-purification capacity of the River Thames in stretches with fewer pollution inputs.
Further investigations needed
Sample point F, which was overall ‘Good’ for E coli but ‘Poor’ for IE, was the only site to see an overall status below ‘Good’. Pangbourne STW could be a possible cause of these higher levels of IE seen throughout the bathing season, but further investigation would be needed to verify this. Thames Water is currently in the process of upgrading this STW, expecting to improve its capacity and reduce the need for untreated discharges during wet weather by 2026.
Thames21 will continue working with local authorities, communities and organisations to raise awareness around safe outdoor swimming access in this region of the Thames. The outcome of this water quality project – data that demonstrates good bacterial water quality at almost all sample points across the bathing season – makes for a nice contrast to the usual doom and gloom of news about poor water quality often seen across rivers in England.
“Many thanks for giving me the opportunity to take part in this sampling project, I have found it extremely interesting and have been pleasantly surprised by the overall cleanliness of the water. It’s not perfect but neither are we swimming in neat raw sewage on top of which a programme like this raises the state of the river in everyone’s mind which should lead to an improvement in the care given to the water” – Citizen scientist, Goring
“Many thanks for giving me the opportunity to take part in this sampling project, I have found it extremely interesting and have been pleasantly surprised by the overall cleanliness of the water. It’s not perfect but neither are we swimming in neat raw sewage on top of which a programme like this raises the state of the river in everyone’s mind which should lead to an improvement in the care given to the water” – Citizen scientist, Goring
