Overflow history upstream of River Thames, Port Meadow, Oxford

The spot's forecast · For event organisers

This page lists the monitored storm overflows upstream of this spot and how often each spilled in each year. It is not a water test, and it does not say whether the water is fit to swim in. It does not include farm runoff, misconnected drains, treated sewage effluent, wildlife or overflows without a monitor. A year's count depends on how long the monitor worked, shown as monitor uptime.

Each year, all overflows upstream

Year	Overflows with a return	Spills	Spill hours	Spill hours, weighted by reach
2021	24	1,046	17,491	500
2022	24	581	7,570	85
2023	29	1,930	29,034	404
2024	29	2,463	38,985	755
2025	29	981	13,757	162

Reach is the share of a spill's bacteria SwimSignal's model expects to arrive here, after die-off on the way and dilution by the river. Weighting by it counts an hour of spilling just upstream for far more than one 40 km away. Spills are counted by the Environment Agency's 12/24 method: any discharge in the first 12 hours counts as one spill, then one more for each 24 hours with any discharge. How reach is worked out.

The overflows, by reach

All 29, the one whose spills matter most here first. Hours away is how long sewage takes to arrive at the model's river speed.

Overflow and id	Company	km upstream	Hours away	Reach	Spills 2023	Spills 2024	Spills 2025	Spill hours 2025	Monitor uptime 2025
Cassington sewage works overflow Cassington STW · TWL00075	Thames Water	4.7	3	81%	2	22	0	0	100%
Combe sewage works overflow Combe STW · TWL00110	Thames Water	19.8	11	8%	111	130	30	356	100%
Finstock sewage works overflow Finstock STW · TWL00184	Thames Water	27.8	15	5%	29	38	13	144	100%
Woodstock sewage works overflow Woodstock STW · TWL00462	Thames Water	18.8	10	4%	59	41	21	89	99%
Charlbury sewage works overflow Charlbury STW · TWL00083	Thames Water	31.3	17	4%	11	22	7	52	100%
Standlake sewage works overflow Standlake STW · TWL00385	Thames Water	20.5	11	3%	131	180	98	2,214	100%
Bampton sewage works overflow Bampton STW · TWL00024	Thames Water	28.5	16	2%	135	160	82	926	99%
Middle Barton sewage works overflow Middle Barton STW · TWL00298	Thames Water	30.6	17	1%	17	44	15	152	100%
Stanton Harcourt sewage works overflow Stanton Harcourt STW · TWL00389	Thames Water	11.5	6	0%	91	123	42	709	100%
Carterton sewage works overflow Carterton STW · TWL00074	Thames Water	34.5	19	0%	61	57	25	404	100%
Bledington sewage works overflow Bledington STW · TWL00042	Thames Water	51.3	28	<1%	65	114	50	947	100%
Church Hanborough sewage works overflow Church Hanborough STW · TWL00098	Thames Water	9.9	6	<1%	120	158	88	1,236	100%
South Leigh sewage works overflow South Leigh STW · TWL00377	Thames Water	12.8	7	<1%	96	71	49	927	100%
Lechlade sewage works overflow Lechlade STW · TWL00263	Thames Water	46.2	26	<1%	45	128	11	161	100%
The Mill (Kingham) pumping station overflow The Mill (Kingham) SPS · TWL00252	Thames Water	52.3	29	<1%	18	23	17	80	100%
Milton-Under-Wychwood sewage works overflow Milton-Under-Wychwood STW · TWL00303	Thames Water	44.8	25	<1%	126	152	67	1,091	100%
Chadlington sewage works overflow Chadlington STW · TWL00079	Thames Water	36.6	20	<1%	64	84	35	362	100%
Clanfield sewage works overflow Clanfield STW · TWL00103	Thames Water	33.8	19	<1%	150	172	14	185	97%
Witney sewage works overflow Witney STW · TWL00457	Thames Water	30.8	17	<1%	119	141	37	576	100%
Faringdon sewage works overflow Faringdon STW · TWL00180	Thames Water	39.3	22	<1%	116	138	50	159	94%
Fairford sewage works overflow Fairford STW · TWL00178	Thames Water	55.5	31	<1%	162	202	107	2,235	100%
XX CSO TWL00575	Thames Water	39.5	22	<1%	34	70	49	54	100%
Highworth sewage works overflow Highworth STW · TWL00227	Thames Water	55.7	31	<1%	60	66	27	340	100%
Kempsford sewage works overflow Kempsford STW · TWL00246	Thames Water	52.8	29	<1%	8	8	0	0	100%
Hannington TWL00130	Thames Water	56.9	32	<1%	21	21	8	14	100%
Chipping Norton sewage works overflow Chipping Norton STW · TWL00094	Thames Water	58.8	33	<1%	28	56	21	277	100%
Kilda Road (Highworth) pumping station overflow Kilda Road (Highworth) SPS · TWL00249	Thames Water	56.1	31	<1%	0	0	0	0	96%
Highworth Eastrop (GWA site) storm overflow Highworth Eastrop CSO (GWA site) · TWL00226	Thames Water	57.3	32	<1%	32	29	9	12	90%
Blunsdon sewage works overflow Blunsdon STW · TWL00046	Thames Water	59.2	33	<1%	19	13	9	54	98%

A dash: no annual return for that overflow in that year.

Sources and credits

Storm overflow annual returns: © Environment Agency copyright and/or database right 2025, Open Government Licence v3.0. Overflow positions: the water companies via the National Storm Overflow Hub, CC BY 4.0. River network: contains OS data © Crown copyright and database right 2026 (OS Open Rivers). Traced and weighted by SwimSignal (swimsignal.co.uk), whose method is at swimsignal.co.uk/methods.html. All credits and licences.