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Ynys Môn - 2025 Sewage

Polluted by sewage 31,610 hours in 2025 - That's 3.66 years

© OpenStreetMap contributors
Contains OS Data © Crown copyright & database right 2021-2024
© Top of the Poops 2021-2024

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View Annual Sewage Data

You're looking at the totals that we have calculated for sewage in Ynys Môn for 2025. It is an estimate, based on very poor quality live data from the Water Companies. This may not align with the 'official' reported sewage values from the water companies, which is reported in April following then end of the year - so 2025 numbers are reported in April 2026.

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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Constituencies near Ynys Môn

Daily Data

Jan - 281 hours
Feb - 1,795 hours
Mar - 1,416 hours
Apr - 979 hours
May - 117 hours
Jun - 538 hours
Jul - 186 hours
Aug - 59 hours
Sept - 2,500 hours
Oct - 1,407 hours
Nov - 10,277 hours
Dec - 12,012 hours
Daily data is experimental and data is not guaranteed to be accurate. Please inform us of any issue, we will fix.
Please note: We don't have rainfall data for Wales. If you know where to source it please let us know!
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Totals so far

Company Site Name Receiving Waterway Overflow Days Total Duration (hours) Offline/Potential Pollution
Dwr Cymru Welsh Water Llanfachraeth WwTW Overflow River Alaw 319 4,467 h 29m -
Dwr Cymru Welsh Water Bryngwran WwTW Overflow Crigyll 161 2,430 h 30m -
Dwr Cymru Welsh Water Green Terrace Llangaffo Storm Overflow Unnamed Ditch 83 1,633 h 11m -
Dwr Cymru Welsh Water Brynsiencyn WwTW Storm Overflow Menai Strait 102 1,575 h 25m -
Dwr Cymru Welsh Water Aberffraw WwTW Storm Overflow Aberffraw Bay 76 1,505 h 30m -
Dwr Cymru Welsh Water Craig Y Don Storm Overflow Afon Goch 81 1,469 h 2m -
Dwr Cymru Welsh Water Menai Llandegfan Storm Overflow Menai Strait 56 1,233 h 5m -
Dwr Cymru Welsh Water Holyhead Porth Y Felin Storm Overflow Unnamed Ditch draining to New Harbour 68 1,183 h 15m -
Dwr Cymru Welsh Water Talwrn Llangefni Storm Overflow Unnamed Ditch 55 1,128 h 15m -
Dwr Cymru Welsh Water Train Station Gaerwen Storm Overflow Tributary of Afon Braint 52 1,103 h 15m -
Dwr Cymru Welsh Water London Road Valley Storm Overflow Unnamed Watercourse 65 1,056 h 45m -
Dwr Cymru Welsh Water Lon Sardis Bodffordd Storm Overflow Cefni Reservoir Bypass Channel 70 986 h 56m -
Dwr Cymru Welsh Water Bull Bay Storm Overflow Bull Bay 66 900 h 30m -
Dwr Cymru Welsh Water Unknown Unknown 36 549 h 28m -
Dwr Cymru Welsh Water Llanfair Pwllgwyngyll WwTW Storm Overflow Menai Strait 83 480 h 30m -
Dwr Cymru Welsh Water Llangaffo WwTW Storm Overflow Unnamed Stream 73 443 h 45m -
Dwr Cymru Welsh Water Pont Y Crug Llanddaniel Storm Overflow Afon Braint 43 430 h 44m -
Dwr Cymru Welsh Water London Road Valley no.2 Storm Overflow Unname Watercourse 52 422 h 30m -
Dwr Cymru Welsh Water Gorsllwyd Llanddona Storm Overflow Afon Cadnant 39 395 h 8m -
Dwr Cymru Welsh Water Llanfaelog Storm Overflow Llyn Maelog 34 382 h 22m -
Dwr Cymru Welsh Water Copperfield Close Four Mile Bridge Storm Overflow Holy Island Straits South 29 377 h -
Dwr Cymru Welsh Water Bae Trearthur Isallt Bach Overflow Caernarfon Bay North 25 364 h 15m -
Dwr Cymru Welsh Water Llaneilian Storm Overflow Coastal Waters 34 362 h 15m -
Dwr Cymru Welsh Water Rhosybol Gorslwyd Storm Overflow Unnamed Watercourse 65 351 h -
Dwr Cymru Welsh Water Llandegfan Menai Bridge Storm Overflow Afon Cadnant 28 347 h 13m -
Dwr Cymru Welsh Water Hermon Malltraeth Storm Overflow Afon Frechwen 27 338 h 28m -
Dwr Cymru Welsh Water Holyhead Bae Trearthur No2 Storm Overflow Unnamed Watercourse 27 316 h 59m -
Dwr Cymru Welsh Water Holyhead Bae Trearthur No1 Storm Overflow Estuarial Waters of the Inland Sea 28 259 h 30m -
Dwr Cymru Welsh Water Holyhead Turkey Shore Storm Overflow Old Harbour Holyhead 65 251 h 15m -
Dwr Cymru Welsh Water Menai Ville Storm Overflow Menai Strait 47 242 h 45m -
Dwr Cymru Welsh Water Afon Goch Lon Parys Amlwch Storm Overflow Afon Goch 37 241 h 30m -
Dwr Cymru Welsh Water Beaumaris & Llanfaes WwTW Storm Overflow Menai Strait 37 240 h -
Dwr Cymru Welsh Water Menai Bridge Faelog Causeway 1 Overflow Menai Strait 44 238 h 15m -
Dwr Cymru Welsh Water Star Gaerwen Storm Overflow Afon Braint 39 236 h 15m -
Dwr Cymru Welsh Water Bodedern Main Storm Overflow River Alaw 26 224 h 45m -
Dwr Cymru Welsh Water Holyhead Morawelon Storm Overflow Outer Harbour, Holyhead 35 206 h 30m -
Dwr Cymru Welsh Water Lon Sardis Storm Overflow River Cefni 54 203 h 32m -
Dwr Cymru Welsh Water Newborough WwTW Storm Overflow Afon Braint 24 180 h -
Dwr Cymru Welsh Water Holyhead WwTW Overflow Unnamed Watercourse 50 178 h 45m -
Dwr Cymru Welsh Water Llanfechell WwTW Storm Overflow Afon Meddanen 14 171 h 15m -
Dwr Cymru Welsh Water Gaerwen WwTW Storm Overflow Afon Cefni 20 166 h 45m -
Dwr Cymru Welsh Water Prince of Wales Road Storm Overflow New Harbour, Holyhead 58 166 h 15m -
Dwr Cymru Welsh Water Ffordd Y Traeth Cemaes Bay Storm Overflow Cemaes Bay 32 161 h -
Dwr Cymru Welsh Water Gorad Beach Road Storm Overflow Estuarial Waters of Afon Alaw 21 158 h 36m -
Dwr Cymru Welsh Water Fryars Bay Llanfaes Overflow Menai Strait 27 145 h -
Dwr Cymru Welsh Water Menai Bridge Suspension Storm Overflow Menai Strait 51 138 h -
Dwr Cymru Welsh Water Menai Suspension Bridge No 3 Overflow Menai Strait 47 131 h 30m -
Dwr Cymru Welsh Water Benllech WwTW Storm Overflow Coastal Waters - Benllech 37 113 h -
Dwr Cymru Welsh Water Llangefni Main Storm Overflow Afon Cefni 16 112 h -
Dwr Cymru Welsh Water Amlwch Port Storm Overflow Coastal Waters - Amlwch Harbour 14 104 h 6m -
Dwr Cymru Welsh Water Brynsciencyn Overflow Menai Strait 12 98 h 17m -
Dwr Cymru Welsh Water Cycle Way Llangefni Storm Overflow Afon Cefni 40 96 h 30m -
Dwr Cymru Welsh Water Unknown Unknown 16 90 h 57m -
Dwr Cymru Welsh Water Brynsiencyn Main Storm Overflow Menai Strait 12 88 h 15m -
Dwr Cymru Welsh Water Malltraeth WwTW Storm Overflow Cefni Estuary 22 87 h 45m -
Dwr Cymru Welsh Water Llangoed Lleiniog Overflow Menai Strait 27 86 h 57m -
Dwr Cymru Welsh Water Moelfre Car Park Storm Overflow Coastal Waters of the Irish Sea 15 55 h 15m -
Dwr Cymru Welsh Water Llandegfan Rhianfa Overflow Menai Strait 20 53 h 26m -
Dwr Cymru Welsh Water Fford Cae Sel Storm Overflow Drainage Ditch 16 50 h -
Dwr Cymru Welsh Water Holyhead Hibernia Row Storm Overflow New Harbour, Holyhead 8 37 h -
Dwr Cymru Welsh Water Beaumaris West End Overflow Menai Strait 10 32 h 30m -
Dwr Cymru Welsh Water Gwalchmai WwTW Storm Overflow Nant Cwyrtai 23 32 h 28m -
Dwr Cymru Welsh Water Beaumaris Green Overflow Estuarial Waters 11 30 h 30m -
Dwr Cymru Welsh Water Pont y Brenin Overflow Afon y Brenin 10 30 h 25m -
Dwr Cymru Welsh Water Beaumaris Green Storm Overflow Menai Strait 10 30 h -
Dwr Cymru Welsh Water Unknown Unknown 18 28 h 15m -
Dwr Cymru Welsh Water Lon Gardener Valley Overflow Unnamed Watercourse 6 28 h -
Dwr Cymru Welsh Water Rhosneigr Overflow Irish Sea 3 27 h 30m -
Dwr Cymru Welsh Water Llansadwrn Anglesy Storm Overflow Afon Cadnant 9 27 h 11m -
Dwr Cymru Welsh Water Plas Y Ffrwd Rhosybol Storm Overflow River Alaw 5 23 h 37m -
Dwr Cymru Welsh Water Rhosneigr Storm Overflow Coastal Waters - Irish Sea 3 18 h -
Dwr Cymru Welsh Water Millbank Storm Overflow Unnamed Watercourse 10 15 h 56m -
Dwr Cymru Welsh Water Llangefni WwTW Storm Overflow Afon Cefni 24 12 h 30m -
Dwr Cymru Welsh Water Malltraeth Overflow Afon Cefni 8 5 h 30m -
Dwr Cymru Welsh Water High Street Malltraeth Storm Overflow Afon Cefni 6 5 h -
Dwr Cymru Welsh Water Benllech Old Tidal Tanks Storm Overflow Coastal Waters - Benllech 3 4 h 29m -
Dwr Cymru Welsh Water Glyn Garth Overflow Menai Strait 5 3 h 35m -
Dwr Cymru Welsh Water Llanfair PG Anglesey No 2 Storm Overflow Menai Strait 6 1 h 29m -
Dwr Cymru Welsh Water Malltraeth WwTW Inlet Storm Overflow Cefni Estuary 1 1 h 13m -
Dwr Cymru Welsh Water Penrhos Beach Holyhead Storm Overflow Beddmanarch Bay 1 0 h 45m -
Dwr Cymru Welsh Water Pentraeth Tan Y Graig Storm Overflow River Nodwydd 2 0 h 30m -
Dwr Cymru Welsh Water Arosfa Road Dwyran Storm Overflow Afon Braint 1 0 h 15m -
Dwr Cymru Welsh Water Llansadwrn Anglesey Storm Overflow Tributary of Afon Cadnant 1 0 h 15m -
Dwr Cymru Welsh Water Llanerchymedd WwTW Storm Overflow River Alaw 1 0 h 15m -
Dwr Cymru Welsh Water Gorwelion Road Newlands Beach Storm Overflow Estuary Afon Alaw 0 0 h -
Dwr Cymru Welsh Water Unknown Unknown 0 0 h -
Dwr Cymru Welsh Water Lon Fain Dwyran Storm Overflow River Braint 0 0 h -
Dwr Cymru Welsh Water Llanfaes Overflow Unnamed Watercourse 0 0 h -
Dwr Cymru Welsh Water Bae Trearthur Lon Isallt Storm Overflow Adjacent Ditch 0 0 h -
Dwr Cymru Welsh Water Unknown Unknown 0 0 h -
Dwr Cymru Welsh Water Waterside Holyhead Storm Overflow New Harbour, Holyhead 0 0 h -
Dwr Cymru Welsh Water Aberffraw Storm Overflow River Ffraw 0 0 h -
Dwr Cymru Welsh Water Llangoed Cynlais Overflow Coastal Waters 0 0 h -
Dwr Cymru Welsh Water Gwalchmai Isaf Storm Overflow Unnamed Watercourse 0 0 h -
Dwr Cymru Welsh Water Menai Bridge Porth Wrach No 2 Overflow Menai Strait 0 0 h -

Data Sources & Accuracy

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.

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Analysing sewage pollution by the Water Industry

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© Openstreetmap contributors, Contains OS data © Crown copyright and database right 2021-2025,
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