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We get information about overflowing CSOs since January 2025. Here is a chart of the last three months of data for Newport West and Islwyn, here you can see overflows in red, the darker the red, the more the CSO overflowed that day.
Each CSO has a row, the most recent data is on the right hand side.
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Donate Now| Company | Site Name | Receiving Waterway | Overflow Days | Total Duration (hours) | Total Duration (days) |
|---|---|---|---|---|---|
| Dwr Cymru Welsh Water | Tanybryn Risca Pontymister Storm Overflow | River Ebbw | 160 | 2,749 h 44m | 114.54 |
| Dwr Cymru Welsh Water | Machen Close St Mellons Storm Overflow | Severn Estuary | 112 | 1,882 h 44m | 78.42 |
| Dwr Cymru Welsh Water | Abercarn Welfare Ground Storm Overflow | River Ebbw | 110 | 1,858 h 15m | 77.42 |
| Dwr Cymru Welsh Water | Western Valley LG Tanks Storm Overflow | Severn Estuary | 60 | 1,325 h 29m | 55.21 |
| Dwr Cymru Welsh Water | Plas Machen Storm Overflow | River Rhymni | 82 | 1,279 h 30m | 53.29 |
| Dwr Cymru Welsh Water | St. Johns Crescent Storm Overflow | River Ebbw | 59 | 575 h 55m | 23.96 |
| Dwr Cymru Welsh Water | Berkerolles Road Storm Overflow | River Ebbw | 37 | 541 h 39m | 22.54 |
| Dwr Cymru Welsh Water | Carnegie Court Storm Overflow | Ebbw Fach River | 78 | 513 h 23m | 21.38 |
| Dwr Cymru Welsh Water | Tredegar Terrace Storm Overflow | Rhynys Brook | 34 | 398 h 22m | 16.58 |
| Dwr Cymru Welsh Water | Maple Avenue Storm Overflow | River Ebbw | 109 | 322 h 37m | 13.42 |
| Dwr Cymru Welsh Water | Waunfawr Park Storm Overflow | River Ebbw | 21 | 223 h 45m | 9.29 |
| Dwr Cymru Welsh Water | Windsor Park Storm Overflow | River Ebbw | 40 | 206 h 18m | 8.58 |
| Dwr Cymru Welsh Water | Cwmgelli Blackwood Storm Overflow | Sirhowy River | 53 | 198 h 42m | 8.25 |
| Dwr Cymru Welsh Water | Brooklands Terrace Storm Overflow | Nant Carn Brook | 37 | 195 h 17m | 8.12 |
| Dwr Cymru Welsh Water | Malvern Terrace Storm Overflow | River Ebbw | 19 | 143 h 6m | 5.96 |
| Dwr Cymru Welsh Water | Tregwilym Close Storm Overflow | River Ebbw | 28 | 124 h 15m | 5.17 |
| Dwr Cymru Welsh Water | Swffryd Storm Overflow | Ebbw Fach River | 65 | 121 h 29m | 5.04 |
| Dwr Cymru Welsh Water | Rhiw Syr Dafydd Hill Storm Overflow | Sirhowy River | 37 | 108 h 15m | 4.5 |
| Dwr Cymru Welsh Water | Woodfield Park Crescent Blackwood Overflow | Sirhowy River | 31 | 105 h 45m | 4.38 |
| Dwr Cymru Welsh Water | Tredegar Street Storm Overflow | Sirhowy River | 12 | 82 h 22m | 3.42 |
| Dwr Cymru Welsh Water | Oakfield Roundabout Storm Overflow | Sirhowy River | 23 | 67 h 14m | 2.79 |
| Dwr Cymru Welsh Water | Commercial Street Risca Storm Overflow | River Ebbw | 24 | 51 h 55m | 2.12 |
| Dwr Cymru Welsh Water | Rock and Fountain Playing fields Storm Overflow | Sirhowy River | 18 | 49 h 52m | 2.04 |
| Dwr Cymru Welsh Water | Pont Gwaith Farm Lane Storm Overflow | Sirhowy River | 6 | 33 h 15m | 1.38 |
| Dwr Cymru Welsh Water | Rifleman Street Storm Overflow | River Ebbw | 40 | 30 h 19m | 1.25 |
| Dwr Cymru Welsh Water | Cardiff Road Newport Overflow | Unnamed Watercourse (via Culvert) | 9 | 27 h 26m | 1.12 |
| Dwr Cymru Welsh Water | Forge Road Bassaleg Storm Overflow | Tributary of Afon Ebbw | 25 | 24 h 42m | 1 |
| Dwr Cymru Welsh Water | Markham Manmoel Crossing Storm Overflow | Sirhowy River | 10 | 22 h 45m | 0.92 |
| Dwr Cymru Welsh Water | Greenfield Road Old Treowen Storm Overflow | River Ebbw | 3 | 22 h 15m | 0.92 |
| Dwr Cymru Welsh Water | Tregwilym Road No 1 Storm Overflow | River Ebbw | 3 | 21 h 30m | 0.88 |
| Dwr Cymru Welsh Water | Thornhill Gardens Storm Overflow | Tributary of Afon Ebbw Fawr | 11 | 19 h 15m | 0.79 |
| Dwr Cymru Welsh Water | Bryngoleu Street Blackwood Overflow | River Rhymni | 9 | 16 h 52m | 0.67 |
| Dwr Cymru Welsh Water | Cwm Road Argoed Storm Overflow | Sirhowy River | 6 | 15 h 11m | 0.62 |
| Dwr Cymru Welsh Water | Carnarvon Drive Storm Overflow | Tributary of Ebbw Fawr | 11 | 14 h 59m | 0.58 |
| Dwr Cymru Welsh Water | South of Aster Close Risca Overflow | River Ebbw | 2 | 7 h 57m | 0.29 |
| Dwr Cymru Welsh Water | High Street Abercarn Storm Overflow | Nant Gwyddon | 20 | 7 h 7m | 0.29 |
| Dwr Cymru Welsh Water | Rogerstone Power Station Land Storm Overflow | River Ebbw | 12 | 3 h 14m | 0.12 |
| Dwr Cymru Welsh Water | Allt-Yr-Yn Avenue Newport Overflow | Unnamed Watercourse | 3 | 1 h 10m | 0.04 |
| Dwr Cymru Welsh Water | Torlais Street Storm Overflow | Unnamed Tribuatary of Afon Ebbw | 1 | 1 h | 0.04 |
| Dwr Cymru Welsh Water | Gladstone Street Crosskeys Storm Overflow | Ebbw Fawr | 1 | 0 h 15m | 0 |
| Dwr Cymru Welsh Water | Hollybush Ancient Druid Storm Overflow | River Sirhowy | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Cobden Street Rear Storm Overflow | River Ebbw | 0 | 0 h | 0 |
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
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.
Get in touch if you have queries or want to discuss our data.
press [at] top-of-the-poops.org