Polluted by sewage 1,725 hours in 2025
What's a potential overflow? If the CSO goes 'Offline' while its Overflowing, we don't know if it stopped overflowing until we get a 'Stop' event.
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Donate Now| Company | Site Name | Receiving Waterway | Overflow Days | Total Duration (hours) | Offline/Potential Pollution |
|---|---|---|---|---|---|
| Dwr Cymru Welsh Water | Tongwynlais Recreation Ground Storm Overflow | River Taff | 65 | 1,161h 2m | - |
| Dwr Cymru Welsh Water | Began Road Cardiff Storm Overflow No2 | River Rhymni | 69 | 379h 59m | - |
| Dwr Cymru Welsh Water | Ynys Bridge 2 Storm Overflow | River Taff | 21 | 111h 40m | - |
| Dwr Cymru Welsh Water | Parc Caedelyn Storm Overflow | Rhydwaedlyd Brook | 19 | 21h 39m | - |
| Dwr Cymru Welsh Water | Began Road Cardiff Storm Overflow | Rhymney | 5 | 18h 41m | - |
| Dwr Cymru Welsh Water | Heathwood Road Storm Overflow | Nant Y Wedal | 17 | 17h 44m | - |
| Dwr Cymru Welsh Water | Westbourne Crescent Bottom Cardiff Storm Overflow | River Taff | 9 | 11h 9m | - |
| Dwr Cymru Welsh Water | Heol Amlwch Storm Overflow | River Taff via culverted watercourse | 5 | 2h 56m | - |
| Dwr Cymru Welsh Water | St. Mellons Bridge Road Storm Overflow | River Rhymni | 1 | 0h 30m | - |
EDM (Event Duration Monitoring) data and Consented Discharges to Controlled Waters with Conditions from Environment Agency & Data Map Wales, and Scottish Water
Experimental derived data from Thames Water API, Some data may be missing or inaccurate. Live sewage data from Stream Water API
Annual figures up to and including 2025 come from official water company returns. The 2026 figure is our own estimate, derived continuously from the companies' live data feeds.
Uses Environment Agency rainfall data from the real-time data API (Beta) - Rainfall data is delayed by up to two days.
This website is intended to provide an accurate representation of the Environment Agency data. The data is hard to use, and thus some errors may have been made. If you find something that is incorrect, please raise an issue at the GitHub issues page and we'll endeavour to fix it quickly.
This project is not associated, approved or endorsed by any of the companies whose logos you see here.