Overflow history upstream of Sandy Lane, Chester
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 | 9 | 259 | 1,367 | 107 |
| 2022 | 10 | 265 | 768 | 33 |
| 2023 | 10 | 369 | 1,809 | 105 |
| 2024 | 10 | 417 | 2,676 | 166 |
| 2025 | 7 | 203 | 883 | 32 |
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 10, 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 |
|---|---|---|---|---|---|---|---|---|---|
| Chester Belgrave Park DCW00021 | Dwr Cymru Welsh Water | 1.4 | under 1 | 93% | 2 | 0 | 0 | 0 | 100% |
| Chester Greenbank DCW00057 | Dwr Cymru Welsh Water | 1.6 | under 1 | 92% | 0 | 0 | 0 | 0 | 100% |
| Chester Eccleston DCW00044 | Dwr Cymru Welsh Water | 3.6 | 2 | 84% | 8 | 15 | – | – | – |
| Aldford storm overflow Aldford CSO · DCW00012 | Dwr Cymru Welsh Water | 8.1 | 4 | 7% | 99 | 107 | 54 | 330 | 100% |
| Tattenhall DCW00037 | Dwr Cymru Welsh Water | 15.7 | 9 | 2% | 91 | 97 | 66 | 336 | 100% |
| Tattenhall Millbrook Park DCW00080 | Dwr Cymru Welsh Water | 16.5 | 9 | 2% | 4 | 5 | – | – | – |
| Chester Huntington Rake & Pickle DCW00117 | Dwr Cymru Welsh Water | 2.2 | 1 | 1% | 2 | 3 | – | – | – |
| Saighton DCW00098 | Dwr Cymru Welsh Water | 7.1 | 4 | 1% | 114 | 121 | 53 | 182 | 100% |
| Tilston DCW00039 | Dwr Cymru Welsh Water | 19.4 | 11 | 1% | 31 | 35 | 14 | 22 | 100% |
| Malpas Whitchurch Road DCW00073 | Dwr Cymru Welsh Water | 49.8 | 28 | <1% | 18 | 34 | 16 | 13 | 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.