Overflow history upstream of River Stour, Dedham
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 | 12 | 278 | 4,070 | 67 |
| 2022 | 16 | 173 | 371 | 7 |
| 2023 | 20 | 519 | 4,418 | 99 |
| 2024 | 21 | 474 | 4,306 | 75 |
| 2025 | 21 | 83 | 544 | 8 |
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 21, 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 |
|---|---|---|---|---|---|---|---|---|---|
| Bures Hamlet pumping station overflow Bures Hamlet-SP · AWS00178 | Anglian Water | 22.1 | 12 | 19% | 5 | 1 | 1 | 3 | 100% |
| Great Cornard sewage works overflow Great Cornard STW · AWS00491 | Anglian Water | 29.6 | 16 | 12% | 0 | 0 | 0 | 0 | 100% |
| Hadleigh sewage works overflow Hadleigh STW · AWS00547 | Anglian Water | 14.2 | 8 | 11% | 45 | 23 | 0 | 0 | 100% |
| Hadleigh sewage works overflow Hadleigh STW · AWS00544 | Anglian Water | 14.2 | 8 | 11% | 0 | 9 | 2 | 14 | 100% |
| Sudbury Great Eastern Road pumping station overflow Sudbury Great Eastern Road Terminal Pumping Station · AWS01331 | Anglian Water | 32.2 | 18 | 11% | 27 | 29 | 20 | 35 | 100% |
| Sudbury The Croft storm overflow Sudbury The Croft CSO · AWS01333 | Anglian Water | 34.0 | 19 | 10% | 25 | 16 | 5 | 1 | 100% |
| Dedham sewage works overflow Dedham STW · AWS00323 | Anglian Water | 0.1 | under 1 | 4% | 1 | 3 | 2 | 10 | 100% |
| Boxford sewage works overflow Boxford STW · AWS00109 | Anglian Water | 15.7 | 9 | 2% | 10 | 25 | 3 | 46 | 100% |
| Boxford-Stone St pumping station overflow Boxford-Stone ST TPS · AWS01306 | Anglian Water | 15.9 | 9 | 2% | 0 | 2 | 0 | 0 | 72% |
| Boxted-Cottage (Suffolk) sewage works overflow Boxted-Cottage (Suffolk) STW · AWS01573 | Anglian Water | 48.7 | 27 | 1% | – | 23 | 3 | 40 | 100% |
| Chelsworth-Cakebridge La pumping station overflow Chelsworth-Cakebridge LA SP · AWS00223 | Anglian Water | 28.0 | 16 | 1% | 8 | 23 | 0 | 0 | 100% |
| Monks Eleigh sewage works overflow Monks Eleigh WRC · AWS00852 | Anglian Water | 28.3 | 16 | 1% | 185 | 147 | 4 | 1 | 100% |
| Lavenham sewage works overflow Lavenham STW PS · AWS00712 | Anglian Water | 35.9 | 20 | 1% | 0 | 15 | 2 | 10 | 100% |
| Lavenham sewage works overflow Lavenham STW · AWS00713 | Anglian Water | 35.9 | 20 | 1% | 45 | 19 | 9 | 32 | 100% |
| Gt Waldingfield-Folley Rd pumping station overflow GT Waldingfield-Folley RD SP · AWS00509 | Anglian Water | 24.8 | 14 | 0% | 21 | 22 | 0 | 0 | 100% |
| Sudbury-Cornard Rd pumping station overflow Sudbury-Cornard RD SP · AWS01330 | Anglian Water | 32.0 | 18 | <1% | 8 | 5 | 0 | 0 | 100% |
| Sudbury Bailey and Coates storm overflow Sudbury Bailey and Coates Combined Sewer Overflow · AWS01332 | Anglian Water | 32.6 | 18 | <1% | 15 | 14 | 2 | 0 | 100% |
| Sudbury sewage works overflow Sudbury Water Recycling Centre · AWS01334 | Anglian Water | 33.8 | 19 | <1% | 0 | 1 | 2 | 2 | 98% |
| Glemsford-Skates Hill pumping station overflow Glemsford-Skates Hill SP · AWS01138 | Anglian Water | 43.6 | 24 | <1% | 8 | 6 | 4 | 8 | 100% |
| Glemsford sewage works overflow Glemsford STW · AWS00469 | Anglian Water | 46.8 | 26 | <1% | 31 | 21 | 4 | 43 | 100% |
| Hundon/Hundon-Lower Church Rd sewage works overflow Hundon STW / Hundon-Lower Church RD TPS · AWS00628 | Anglian Water | 56.9 | 32 | <1% | 85 | 70 | 20 | 300 | 100% |
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.