Overflow history upstream of Wallingford Beach, River Thames

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	36	1,511	20,363	83
2022	36	647	7,848	18
2023	41	2,128	29,628	92
2024	41	3,216	49,925	328
2025	41	1,079	14,659	70

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 41, 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
Dorchester sewage works overflow Dorchester STW · TWL00157	Thames Water	7.8	4	20%	4	63	15	121	100%
Heyford Hill Lane (Littlemore) pumping station overflow Heyford Hill Lane (Littlemore) SPS · TWL00273	Thames Water	33.0	18	9%	5	26	1	6	100%
Cassington sewage works overflow Cassington STW · TWL00075	Thames Water	45.2	25	2%	2	22	0	0	100%
Shabbington sewage works overflow Shabbington STW · TWL00363	Thames Water	39.6	22	2%	48	67	23	322	88%
Islip sewage works overflow Islip STW · TWL00244	Thames Water	48.4	27	1%	70	61	34	697	100%
Drayton sewage works overflow Drayton STW · TWL00162	Thames Water	22.5	12	1%	116	128	47	639	100%
Benson sewage works overflow Benson STW · TWL00034	Thames Water	1.5	under 1	1%	12	101	18	361	97%
Didcot sewage works overflow Didcot STW · TWL00155	Thames Water	18.0	10	1%	61	94	26	339	100%
Stanford in the Vale sewage works overflow Stanford in the Vale STW · TWL00387	Thames Water	43.1	24	1%	2	0	3	6	100%
Charlton-on-Otmoor sewage works overflow Charlton-on-Otmoor STW · TWL00085	Thames Water	53.4	30	0%	77	120	54	814	100%
Oxford sewage works overflow Oxford STW · TWL00323	Thames Water	33.0	18	<1%	133	162	43	590	100%
Long Crendon sewage works overflow Long Crendon STW · TWL00276	Thames Water	46.8	26	<1%	3	19	0	0	100%
Haddenham sewage works overflow Haddenham STW · TWL00207	Thames Water	49.5	28	<1%	19	76	37	552	99%
Culham sewage works overflow Culham STW · TWL00147	Thames Water	13.4	7	<1%	32	78	38	378	100%
Worminghall sewage works overflow Worminghall STW · TWL00464	Thames Water	37.0	20	<1%	52	93	23	264	100%
The willows, north hinksey lane TWL00411	Thames Water	38.4	21	<1%	11	8	7	48	100%
Forest Hill sewage works overflow Forest Hill STW · TWL00188	Thames Water	33.8	19	<1%	3	5	3	4	100%
West way, botley (syphon) TWL00439	Thames Water	39.2	22	<1%	26	18	10	40	96%
Little Milton sewage works overflow Little Milton STW · TWL00271	Thames Water	22.1	12	<1%	68	168	64	1,310	98%
Watlington sewage works overflow Watlington STW · TWL00433	Thames Water	28.9	16	<1%	8	90	30	137	100%
Appleton sewage works overflow Appleton STW · TWL00013	Thames Water	34.9	19	<1%	121	160	17	159	100%
Horton-Cum-Studley sewage works overflow Horton-Cum-Studley STW · TWL00238	Thames Water	38.0	21	<1%	55	76	38	462	99%
Wantage sewage works overflow Wantage STW · TWL00425	Thames Water	35.6	20	<1%	78	96	30	170	100%
Wheatley sewage works overflow Wheatley STW · TWL00446	Thames Water	27.5	15	<1%	124	160	76	1,125	100%
Abingdon sewage works overflow Abingdon STW · TWL00004	Thames Water	22.1	12	<1%	38	85	13	112	100%
Tubney XX pumping station overflow Tubney SPS XX · TWL00806	Thames Water	34.6	19	<1%	0	7	1	1	100%
Tetsworth sewage works overflow Tetsworth STW · TWL00408	Thames Water	33.5	19	<1%	36	30	6	42	100%
Chalgrove sewage works overflow Chalgrove STW · TWL00080	Thames Water	25.5	14	<1%	132	147	8	56	100%
Thame sewage works overflow Thame STW · TWL00409	Thames Water	45.6	25	<1%	38	105	30	460	100%
Stone sewage works overflow Stone STW · TWL00392	Thames Water	56.1	31	<1%	145	157	44	653	98%
Dorton sewage works overflow Dorton STW · TWL00160	Thames Water	56.7	32	<1%	46	54	12	44	93%
Uffington sewage works overflow Uffington STW · TWL00419	Thames Water	50.6	28	<1%	86	101	48	654	100%
Kingston Bagpuize sewage works overflow Kingston Bagpuize STW · TWL00257	Thames Water	37.2	21	<1%	25	143	32	389	100%
Weston-on-the-Green sewage works overflow Weston-on-the-Green STW · TWL00443	Thames Water	52.7	29	<1%	63	86	42	696	100%
Stanton Harcourt sewage works overflow Stanton Harcourt STW · TWL00389	Thames Water	52.0	29	<1%	91	123	42	709	100%
Church Hanborough sewage works overflow Church Hanborough STW · TWL00098	Thames Water	50.5	28	<1%	120	158	88	1,236	100%
Manor Farm Road (Sydenham) pumping station overflow Manor Farm Road (Sydenham) SPS · TWL00289	Thames Water	52.3	29	<1%	1	4	0	0	100%
Weston-on-the-Green pumping station overflow Weston-on-the-Green SPS · TWL00442	Thames Water	52.6	29	<1%	0	3	2	21	100%
Beckley sewage works overflow Beckley STW · TWL00113	Thames Water	53.9	30	<1%	22	10	4	24	100%
South Leigh sewage works overflow South Leigh STW · TWL00377	Thames Water	53.3	30	0%	96	71	49	927	100%
Woodstock sewage works overflow Woodstock STW · TWL00462	Thames Water	59.4	33	0%	59	41	21	89	99%

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.