Thames Water released untreated sewage from multiple storm overflows across Oxfordshire in the days after rainfall on Monday 7 September, with discharges entering brooks and streams that all ultimately feed the River Thames and the North Sea, according to a map published by SewageMap.co.uk and reported on 9 September (Bicester Advertiser). One release in Milton-Under-Wychwood ran from 8.30pm to 10pm on 7 September into Littlestock Brook, which then flows to the River Evenlode and the Thames (Bicester Advertiser). A separate 45-minute release on the Monday morning upstream of Aylesbury was later tracked roughly 80 miles downstream to Kingston-upon-Thames, as mapped on 16 September (Oxford Mail).
Key takeaways
- Thames Water discharged untreated sewage from at least three Oxfordshire storm overflows after rainfall on Monday 7 September, reported on 9 September (Bicester Advertiser).
- One discharge in Milton-Under-Wychwood ran for 1.5 hours (8.30pm to 10pm) into Littlestock Brook, which feeds the River Evenlode and then the Thames (Bicester Advertiser).
- A separate 45-minute Thames Water release on the Monday morning near Stewkley was tracked approximately 80 miles downstream to Kingston-upon-Thames (Oxford Mail).
- Thames Water said it will deliver the largest upgrade to its wastewater network in 150 years over the next five years, including increased treatment capacity, fewer storm discharges and new nutrient reduction schemes (Bicester Advertiser).
- Surfers Against Sewage had logged 764 sewage alerts at 244 bathing sites in England and Wales since the bathing season opened on 15 May, with 43% of 573 bathing sites receiving warnings so far in 2026 (Bicester Advertiser).
What happened
Rain on Monday 7 September triggered storm overflow operation at three Oxfordshire sites tracked on SewageMap.co.uk. In Milton-Under-Wychwood, untreated sewage entered Littlestock Brook from 8.30pm to 10pm, with the receiving water going on to the River Evenlode and then the Thames (Bicester Advertiser). That same Littlestock Brook overflow has recorded 1,230 hours and 30 minutes of discharge since the start of 2026, according to SewageMap.co.uk data published on 9 September (Bicester Advertiser).
A second overflow at Henton Stream in Chinnor discharged for four minutes on the morning of 9 September, taking the Cuttle Brook system into the River Thame catchment and then the Thames (Bicester Advertiser). The Chinnor spot has logged 801 hours and 40 minutes of discharge since 1 January 2026 (Bicester Advertiser). A third overflow at Faringdon Stream ran from 8.45 to 9.15 on 7 September, with flow heading north then north-west to the Thames near Radcot, and east along the Thames through Oxford, Abingdon, Reading and London to the tidal estuary and the North Sea (Bicester Advertiser).
A wider Thames Water release on the same Monday morning, near Stewkley above Aylesbury, was tracked approximately 80 miles downstream via Hardwick Brook, the River Thame near Aylesbury, the Thames near Dorchester-on-Thames, and then through Abingdon, Reading, Henley, Maidenhead, Slough and to Kingston-upon-Thames, as reported on 16 September (Oxford Mail).
A Thames Water spokesperson said: "Storm overflows operate within Environment Agency limits and are a legally permitted part of the wastewater system. They help prevent sewage backing up into homes during heavy rainfall, with permitted discharges diluted by rainwater. Over the next five years, we will deliver the largest upgrade to our wastewater network in 150 years, including increased treatment capacity, fewer storm discharges and new nutrient reduction schemes." (Bicester Advertiser).
The company also said 2024 saw some of the largest sewage discharges in recent history, and that recent investment is showing results, as reported on 9 September (Bicester Advertiser). A Department for Environment, Food and Rural Affairs spokesperson said: "The Government shares the public's frustration that discharges are polluting our rivers, lakes and seas. Storm overflows should only be used in very specific circumstances, and this Government has already taken action against water companies who are failing to perform, making it a criminal offence to cover up illegal sewage spills." (Bicester Advertiser).
Discharge events reported in September 2026
| Site | Receiving water | Reported duration | Start time | 2026 cumulative hours | Source |
|---|---|---|---|---|---|
| Milton-Under-Wychwood (Littlestock Brook) | River Evenlode, then Thames | 1 h 30 min | 8.30pm, Mon 7 Sept | 1,230 h 30 min | Bicester Advertiser |
| Henton Stream, Chinnor | River Thame catchment, then Thames | 4 min | morning of 9 Sept | 801 h 40 min | Bicester Advertiser |
| Faringdon Stream | Thames near Radcot | 30 min | 8.45, Mon 7 Sept | not reported | Bicester Advertiser |
| Stewkley, above Aylesbury | Hardwick Brook, River Thame, Thames to Kingston-upon-Thames | 45 min | Monday morning, 7 Sept week | not reported | Oxford Mail |
Specification read
The reported event is a storm overflow activation, not a treatment-plant capacity failure, so the procurement signal sits in the front of the works rather than the biological or tertiary stage. The 1,230 h 30 min cumulative figure for the Milton-Under-Wychwood spot since 1 January 2026 (Bicester Advertiser) implies a sustained hydraulic overload at combined-sewer catchments upstream of the Evenlode, with overflow volumes that are not stated in the sources and so cannot be converted to m³/day here. As a benchmark for the size of plant this class of catchment typically ties into, Municipal treatment works feeding the upper Thames commonly sit in the tens of thousands of m³/day range, with population equivalents in the low hundreds of thousands; specific flows and loads for the Oxfordshire sites named are not reported and so any number given here would be a (general industry range, not from the sources). The treatment train this class of upgrade bears on is screening, grit removal and primary clarification, followed by a biological stage such as Integrated Sewage Treatment using A2O, MBR, MBBR, SBR or UASB, then tertiary solids removal and disinfection, with nutrient reduction and, where consent requires, DAF or ZLD polishing. Thames Water's own statement of intent covers increased treatment capacity, fewer storm discharges and new nutrient reduction schemes, so the immediate spend line is in primary, biological and nutrient-removal upgrades rather than disinfection (Bicester Advertiser). For a plant manager or procurement lead, the recognition sentence is: if your works serves a combined-sewer catchment in the order of 50,000 to 200,000 m³/day with BOD in the 150 to 300 mg/L range, and you are seeing repeated storm-overflow activations during routine rainfall, this is the class of upgrade that Thames Water is signalling it will procure over the next five years (Bicester Advertiser); see also the MBR vs Conventional Activated Sludge for Fabricated Metals Wastewater in Two Rivers (2026 Guide) and MBR vs Conventional Activated Sludge for Chemicals Wastewater in Gulfport: 2026 Engineering Comparison for the biological-stage trade-offs buyers typically weigh in this kind of upgrade.
FAQ
What actually happened in Oxfordshire in the week of 7 September 2026?
Thames Water storm overflows released untreated sewage at at least three Oxfordshire sites after rainfall on Monday 7 September, with flows entering brooks that feed the River Evenlode, the River Thame catchment, the Thames at Radcot and, in a separate event, a 45-minute release that reached Kingston-upon-Thames roughly 80 miles downstream (Bicester Advertiser, Oxford Mail).
What is Thames Water planning to upgrade?
Thames Water said it will deliver the largest upgrade to its wastewater network in 150 years over the next five years, covering increased treatment capacity, fewer storm discharges and new nutrient reduction schemes (Bicester Advertiser). Specific contract values, lead times or awarded suppliers are not reported and would be a (general industry range, not from the sources).
How big is the storm overflow problem nationally?
Surfers Against Sewage recorded 764 sewage alerts at 244 bathing sites in England and Wales since the official bathing season opened on 15 May, and 43% of 573 bathing sites have received warnings so far in 2026 (Bicester Advertiser). The bathing season runs until 30 September.
Which treatment stage should a buyer focus on for this class of upgrade?
Given that the reported event is a hydraulic storm-overflow issue and Thames Water's stated scope is treatment capacity, fewer discharges and nutrient reduction, the relevant stages are primary capacity, biological treatment (A2O, MBR, MBBR, SBR or UASB) and nutrient removal, rather than disinfection. Specific flow, BOD and consent figures for the Oxfordshire sites are not reported in the sources.
