Polluted by sewage 33,527 hours in 2025 - That's 3.88 years
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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 Bangor Aberconwy, 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 | Cwm Penmachno WwTW Storm Overflow | River Machno | 230 | 5,176 h 31m | 215.67 |
| Dwr Cymru Welsh Water | Dolwyddelan WwTW Storm Overflow | Afon Lledr | 168 | 3,004 h 40m | 125.17 |
| Dwr Cymru Welsh Water | Capel Curig WwTW Storm Overflow | Afon Lliw | 192 | 2,294 h 36m | 95.58 |
| Dwr Cymru Welsh Water | Cwm Penmachno Storm Overflow | unnamed ditch | 110 | 1,743 h 45m | 72.62 |
| Dwr Cymru Welsh Water | Talybont WwTW Storm Overflow | River Dulyn | 97 | 1,619 h 20m | 67.46 |
| Dwr Cymru Welsh Water | Tregarth WwTW Storm Overflow | Afon Ogwen | 96 | 1,613 h 30m | 67.21 |
| Dwr Cymru Welsh Water | Trefriw WwTW Storm Overflow | River Crafnant | 101 | 1,560 h 29m | 65 |
| Dwr Cymru Welsh Water | Bethesda WwTW Storm Overflow | River Ogwen | 114 | 1,273 h 15m | 53.04 |
| Dwr Cymru Welsh Water | Llangernyw WwTW Overflow | Elwy | 71 | 1,102 h 6m | 45.92 |
| Dwr Cymru Welsh Water | Betws Yn Rhos WwTW Storm Overflow | Tributary of Afon Dulas | 63 | 1,085 h 46m | 45.21 |
| Dwr Cymru Welsh Water | Penmaenmawr WwTW Storm Overflow | Coastal Waters - Conwy Bay | 64 | 1,048 h 12m | 43.67 |
| Dwr Cymru Welsh Water | Bangor Treborth WwTW Storm Overflow | Menai Strait | 68 | 966 h 3m | 40.25 |
| Dwr Cymru Welsh Water | Llanrwst WwTW Settled Storm Overflow | River Conwy | 66 | 934 h | 38.92 |
| Dwr Cymru Welsh Water | Mill Road Betws-Y-Coed Storm Overflow | Afon Lliw | 48 | 842 h 59m | 35.08 |
| Dwr Cymru Welsh Water | Betws-Y-Coed Storm Overflow | River Conwy | 71 | 822 h 7m | 34.25 |
| Dwr Cymru Welsh Water | Tregarth Bron Ogwen Storm Overflow | Afon Ogwen | 41 | 679 h 35m | 28.29 |
| Dwr Cymru Welsh Water | Llan Penmachno WwTW Storm Overflow | River Machno | 58 | 596 h 15m | 24.83 |
| Dwr Cymru Welsh Water | Rock Terrace Storm Overflow | River Ogwen | 63 | 534 h | 22.25 |
| Dwr Cymru Welsh Water | Aber Storm Overflow | Menai Strait | 31 | 479 h | 19.96 |
| Dwr Cymru Welsh Water | Pwll-Glas WwTW Storm Overflow | River Clwyd | 40 | 460 h 45m | 19.17 |
| Dwr Cymru Welsh Water | Eglwysbach WwTW Storm Overflow | River Hiraethlyn | 25 | 383 h 30m | 15.96 |
| Dwr Cymru Welsh Water | Rowen WwTW Storm Overflow | Afon Roe | 77 | 381 h 18m | 15.88 |
| Dwr Cymru Welsh Water | Llanrwst WwTW Storm Overflow | River Conwy | 72 | 374 h 30m | 15.58 |
| Dwr Cymru Welsh Water | Betws-Y-Coed Pentre Ddu Storm Overflow | Afon Lliw | 38 | 355 h 59m | 14.79 |
| Dwr Cymru Welsh Water | Trefriw Main Storm Overflow | River Conwy | 48 | 353 h 44m | 14.71 |
| Dwr Cymru Welsh Water | Betws-Y-Coed WwTW Storm Overflow | Afon Lliw | 69 | 267 h 28m | 11.12 |
| Dwr Cymru Welsh Water | Glasinfryn Storm Overflow | Afon Cegin | 38 | 265 h | 11.04 |
| Dwr Cymru Welsh Water | Pendraw R Llan Glan Conwy Storm Overflow | River Conwy | 17 | 238 h 45m | 9.92 |
| Dwr Cymru Welsh Water | B5382 Llangernyw Storm Overflow | River Elwy | 42 | 229 h 6m | 9.54 |
| Dwr Cymru Welsh Water | Dolwyddelan Storm Overflow | Afon Lledr | 31 | 187 h 42m | 7.79 |
| Dwr Cymru Welsh Water | Cerrigydrudion WwTW Storm Overflow | Afon Nug | 46 | 182 h 10m | 7.58 |
| Dwr Cymru Welsh Water | Tyn-y-Groes WwTW Storm Overflow | River Conwy | 31 | 176 h 36m | 7.33 |
| Dwr Cymru Welsh Water | Llanfairfechan Park Crescent Storm Overflow | Afon Llanfairfechan | 71 | 172 h 48m | 7.17 |
| Dwr Cymru Welsh Water | Marine Crescent Deganwy Storm Overflow | Estuarial Waters of the River Conwy | 55 | 166 h | 6.92 |
| Dwr Cymru Welsh Water | Gwydyr Road Dolgarrog Storm Overflow | River Conwy | 26 | 163 h 13m | 6.79 |
| Dwr Cymru Welsh Water | Clawddnewydd WwTW Storm Overflow | Tributary of the Nant-Y-Cefn | 18 | 155 h 45m | 6.46 |
| Dwr Cymru Welsh Water | Maes Bleddyn Storm Overflow | Tributary of Afon Ogwen | 34 | 138 h 45m | 5.75 |
| Dwr Cymru Welsh Water | Penrhyn-Isaf Road Penrhyn Bay Storm Overflow | Penrhyn Bay | 58 | 127 h 35m | 5.29 |
| Dwr Cymru Welsh Water | Waterloo Bridge Storm Overflow | River Conwy | 19 | 117 h 7m | 4.88 |
| Dwr Cymru Welsh Water | Llanllechid Overflow | Afon-y-Llan | 11 | 114 h 45m | 4.75 |
| Dwr Cymru Welsh Water | Morfa Road Penrhyn Bay Storm Overflow | Coastal Waters - Penrhyn Bay | 17 | 104 h 10m | 4.33 |
| Dwr Cymru Welsh Water | Pwll-Glas WwTW Inlet Storm Overflow | River Clwyd | 16 | 90 h 30m | 3.75 |
| Dwr Cymru Welsh Water | Nebo Road Llanrwst Storm Overflow | Afon Nant-y-Goron | 47 | 67 h 9m | 2.79 |
| Dwr Cymru Welsh Water | Tan Y Ffordd Dolgarrog Storm Overflow | River Conwy | 22 | 66 h 30m | 2.75 |
| Dwr Cymru Welsh Water | Rhostrehwfa Storm Overflow | River Cledwen | 14 | 66 h | 2.75 |
| Dwr Cymru Welsh Water | Llandudno West Shore Storm Overflow | Conwy Bay | 13 | 63 h 15m | 2.62 |
| Dwr Cymru Welsh Water | Llanrwst Storm Overflow | River Conwy | 5 | 62 h 44m | 2.58 |
| Dwr Cymru Welsh Water | Pentrefoelas WwTW Storm Overflow | Afon Merddwr | 10 | 60 h 14m | 2.5 |
| Dwr Cymru Welsh Water | Llanfair Talhaiarn WwTW Storm Overflow | River Elwy | 17 | 58 h | 2.42 |
| Dwr Cymru Welsh Water | Dale Road Storm Overflow | Conwy Bay | 51 | 55 h 51m | 2.29 |
| Dwr Cymru Welsh Water | Glanwydden Storm Overflow | Afon Wydden | 12 | 54 h 45m | 2.25 |
| Dwr Cymru Welsh Water | Tan-y-Fedw Trefriw Storm Overflow | Afon Crafnant | 15 | 49 h 9m | 2.04 |
| Dwr Cymru Welsh Water | Llanfairfechan No 1 Storm Overflow | Afon Llanfairfechan | 33 | 47 h 38m | 1.96 |
| Dwr Cymru Welsh Water | Marl Drive Llandudno Storm Overflow | Afon Wydden | 6 | 31 h | 1.29 |
| Dwr Cymru Welsh Water | TalyBont WwTW Storm Overflow | Afon Ogwen | 13 | 25 h 45m | 1.04 |
| Dwr Cymru Welsh Water | Betws-Y-Coed Muriau Storm Overflow | River Conwy | 21 | 25 h 25m | 1.04 |
| Dwr Cymru Welsh Water | Conwy Gyffin Storm Overflow | River Conwy | 17 | 23 h 30m | 0.96 |
| Dwr Cymru Welsh Water | Llandudno Junction Glan-Y-Mor Road Storm Overflow | Estuarial Waters of the River Conwy | 10 | 22 h 45m | 0.92 |
| Dwr Cymru Welsh Water | Beach Road Bangor Storm Overflow | Menai Strait | 8 | 20 h | 0.83 |
| Dwr Cymru Welsh Water | Lower Gate Street Conwy Storm Overflow | River Conwy Estuary | 8 | 20 h | 0.83 |
| Dwr Cymru Welsh Water | Bangor Beach Road Overflow | Menai Strait | 6 | 14 h | 0.58 |
| Dwr Cymru Welsh Water | Treborth Bangor WwTW Overflow | Menai Strait | 8 | 14 h | 0.58 |
| Dwr Cymru Welsh Water | Morfa Drive Conwy Storm Overflow | River Conwy | 10 | 13 h 30m | 0.54 |
| Dwr Cymru Welsh Water | Penaenmawr Station Storm Overflow | Coastal waters via a culvert | 7 | 12 h 1m | 0.5 |
| Dwr Cymru Welsh Water | Conwy Harbour Overflow | River Conwy | 8 | 10 h 50m | 0.42 |
| Dwr Cymru Welsh Water | Penmaenmawr WwTW Overflow | Conwy Bay | 4 | 8 h 45m | 0.33 |
| Dwr Cymru Welsh Water | Penmaenmawr Promenade Storm Overflow | Coastal Waters - Penmaenmawr | 4 | 8 h 15m | 0.33 |
| Dwr Cymru Welsh Water | Glan Y Mor Road Deganwy Tywyn Storm Overflow | River Conwy | 8 | 7 h 15m | 0.29 |
| Dwr Cymru Welsh Water | Llandudno Road Penrhyn Bay Storm Overflow | Afon Ganol | 8 | 7 h 14m | 0.29 |
| Dwr Cymru Welsh Water | Hill View Road Llanrhos Storm Overflow | Unnamed Ditch | 6 | 7 h 12m | 0.29 |
| Dwr Cymru Welsh Water | Penrhyn Hill Storm Overflow | Coastal Waters - Penrhyn Bay | 10 | 6 h | 0.25 |
| Dwr Cymru Welsh Water | Llandudno Conway Road Storm Overflow | Afon Wydden | 2 | 3 h 19m | 0.12 |
| Dwr Cymru Welsh Water | Coleg Normal Overflow | Menai Strait | 4 | 3 h 15m | 0.12 |
| Dwr Cymru Welsh Water | Pentre Llanrhaeadr Storm Overflow | Nant Mawr | 1 | 2 h 45m | 0.08 |
| Dwr Cymru Welsh Water | Llansannan Storm Overflow | River Aled | 3 | 2 h 30m | 0.08 |
| Dwr Cymru Welsh Water | Deganwy Deganwy Road Storm Overflow | Conwy Estuary | 3 | 1 h 44m | 0.04 |
| Dwr Cymru Welsh Water | Biwla Storm Overflow | Nant Garreg Ddu | 3 | 1 h 15m | 0.04 |
| Dwr Cymru Welsh Water | Pentre Felin Betws Y Coed Overflow | Afon Lliw | 2 | 0 h 28m | 0 |
| Dwr Cymru Welsh Water | Unknown | Unknown | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Ganol Overflow | Afon Ganol | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Unknown | Unknown | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Meirion Road Storm Overflow | Estuarial Waters | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Hendre Road Conwy Storm Overflow | Afon Gyffin | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Glan Traeth Bangor Overflow | Afon Cegin | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Near Penmaenmawr Dwygyfylchi Storm Overflow | Afon Gyrach | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Tremarl Llandudno Junction Overfow | Unname Watercourse | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Gorad Road Bangor Storm Overflow | Menai Strait | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | King Georges Field Overflow | Culvert to Bangor Mud Flats | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Llandudno Road Penrhyn Bay Overflow | Afon Ganol East | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Unknown | Unknown | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Mill Hill Storm Overflow | Afon Gyffin | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Betws-Yn-Rhos Recreation Ground Storm Overflow | River Dulas | 0 | 0 h | 0 |
| Dwr Cymru Welsh Water | Ganol Disinfected Overflow | Afon Ganol | 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.