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Ynys Môn - 2025 Sewage

Polluted by sewage 31,659 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 - 205 hours
Aug - 75 hours
Sept - 2,517 hours
Oct - 1,405 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 4,497h 4m -
Dwr Cymru Welsh Water Bryngwran WwTW Overflow Crigyll 161 2,431h 42m -
Dwr Cymru Welsh Water Green Terrace Llangaffo Storm Overflow Unnamed Ditch 83 1,632h 58m -
Dwr Cymru Welsh Water Brynsiencyn WwTW Storm Overflow Menai Strait 102 1,574h 12m -
Dwr Cymru Welsh Water Aberffraw WwTW Storm Overflow Aberffraw Bay 76 1,505h 19m -
Dwr Cymru Welsh Water Craig Y Don Storm Overflow Afon Goch 81 1,469h 40m -
Dwr Cymru Welsh Water Menai Llandegfan Storm Overflow Menai Strait 56 1,232h 46m -
Dwr Cymru Welsh Water Holyhead Porth Y Felin Storm Overflow Unnamed Ditch draining to New Harbour 68 1,183h 18m -
Dwr Cymru Welsh Water Talwrn Llangefni Storm Overflow Unnamed Ditch 55 1,127h 37m -
Dwr Cymru Welsh Water Train Station Gaerwen Storm Overflow Tributary of Afon Braint 52 1,103h 15m -
Dwr Cymru Welsh Water London Road Valley Storm Overflow Unnamed Watercourse 65 1,056h 32m -
Dwr Cymru Welsh Water Lon Sardis Bodffordd Storm Overflow Cefni Reservoir Bypass Channel 70 986h 58m -
Dwr Cymru Welsh Water Bull Bay Storm Overflow Bull Bay 66 900h 30m -
Dwr Cymru Welsh Water Unknown Unknown 36 550h 2m -
Dwr Cymru Welsh Water Llanfair Pwllgwyngyll WwTW Storm Overflow Menai Strait 83 486h 41m -
Dwr Cymru Welsh Water Llangaffo WwTW Storm Overflow Unnamed Stream 73 446h 2m -
Dwr Cymru Welsh Water Pont Y Crug Llanddaniel Storm Overflow Afon Braint 43 429h 48m -
Dwr Cymru Welsh Water London Road Valley no.2 Storm Overflow Unname Watercourse 52 423h 25m -
Dwr Cymru Welsh Water Gorsllwyd Llanddona Storm Overflow Afon Cadnant 39 393h 55m -
Dwr Cymru Welsh Water Llanfaelog Storm Overflow Llyn Maelog 34 382h 4m -
Dwr Cymru Welsh Water Copperfield Close Four Mile Bridge Storm Overflow Holy Island Straits South 29 377h 16m -
Dwr Cymru Welsh Water Bae Trearthur Isallt Bach Overflow Caernarfon Bay North 25 364h 15m -
Dwr Cymru Welsh Water Llaneilian Storm Overflow Coastal Waters 34 362h 32m -
Dwr Cymru Welsh Water Rhosybol Gorslwyd Storm Overflow Unnamed Watercourse 65 350h 40m -
Dwr Cymru Welsh Water Llandegfan Menai Bridge Storm Overflow Afon Cadnant 28 347h 9m -
Dwr Cymru Welsh Water Hermon Malltraeth Storm Overflow Afon Frechwen 27 338h 27m -
Dwr Cymru Welsh Water Holyhead Bae Trearthur No2 Storm Overflow Unnamed Watercourse 27 316h 59m -
Dwr Cymru Welsh Water Holyhead Bae Trearthur No1 Storm Overflow Estuarial Waters of the Inland Sea 28 259h 30m -
Dwr Cymru Welsh Water Holyhead Turkey Shore Storm Overflow Old Harbour Holyhead 65 251h 24m -
Dwr Cymru Welsh Water Menai Ville Storm Overflow Menai Strait 47 242h 57m -
Dwr Cymru Welsh Water Afon Goch Lon Parys Amlwch Storm Overflow Afon Goch 37 241h 20m -
Dwr Cymru Welsh Water Beaumaris & Llanfaes WwTW Storm Overflow Menai Strait 37 239h 47m -
Dwr Cymru Welsh Water Menai Bridge Faelog Causeway 1 Overflow Menai Strait 44 238h 27m -
Dwr Cymru Welsh Water Star Gaerwen Storm Overflow Afon Braint 39 236h 23m -
Dwr Cymru Welsh Water Bodedern Main Storm Overflow River Alaw 26 224h 57m -
Dwr Cymru Welsh Water Holyhead Morawelon Storm Overflow Outer Harbour, Holyhead 35 206h 6m -
Dwr Cymru Welsh Water Lon Sardis Storm Overflow River Cefni 54 204h 57m -
Dwr Cymru Welsh Water Holyhead WwTW Overflow Unnamed Watercourse 50 181h 27m -
Dwr Cymru Welsh Water Newborough WwTW Storm Overflow Afon Braint 24 180h 12m -
Dwr Cymru Welsh Water Llanfechell WwTW Storm Overflow Afon Meddanen 14 171h 33m -
Dwr Cymru Welsh Water Gaerwen WwTW Storm Overflow Afon Cefni 20 166h 45m -
Dwr Cymru Welsh Water Prince of Wales Road Storm Overflow New Harbour, Holyhead 58 165h 35m -
Dwr Cymru Welsh Water Ffordd Y Traeth Cemaes Bay Storm Overflow Cemaes Bay 32 161h 54m -
Dwr Cymru Welsh Water Gorad Beach Road Storm Overflow Estuarial Waters of Afon Alaw 21 159h 30m -
Dwr Cymru Welsh Water Fryars Bay Llanfaes Overflow Menai Strait 27 143h 50m -
Dwr Cymru Welsh Water Menai Bridge Suspension Storm Overflow Menai Strait 52 138h 28m -
Dwr Cymru Welsh Water Menai Suspension Bridge No 3 Overflow Menai Strait 48 131h 58m -
Dwr Cymru Welsh Water Benllech WwTW Storm Overflow Coastal Waters - Benllech 37 112h 51m -
Dwr Cymru Welsh Water Llangefni Main Storm Overflow Afon Cefni 16 111h 49m -
Dwr Cymru Welsh Water Amlwch Port Storm Overflow Coastal Waters - Amlwch Harbour 14 105h 12m -
Dwr Cymru Welsh Water Cycle Way Llangefni Storm Overflow Afon Cefni 40 98h 12m -
Dwr Cymru Welsh Water Brynsciencyn Overflow Menai Strait 12 98h -
Dwr Cymru Welsh Water Unknown Unknown 16 92h 16m -
Dwr Cymru Welsh Water Brynsiencyn Main Storm Overflow Menai Strait 12 88h 26m -
Dwr Cymru Welsh Water Malltraeth WwTW Storm Overflow Cefni Estuary 22 88h 9m -
Dwr Cymru Welsh Water Llangoed Lleiniog Overflow Menai Strait 27 86h 58m -
Dwr Cymru Welsh Water Moelfre Car Park Storm Overflow Coastal Waters of the Irish Sea 15 55h 54m -
Dwr Cymru Welsh Water Llandegfan Rhianfa Overflow Menai Strait 20 53h 27m -
Dwr Cymru Welsh Water Fford Cae Sel Storm Overflow Drainage Ditch 16 50h 40m -
Dwr Cymru Welsh Water Holyhead Hibernia Row Storm Overflow New Harbour, Holyhead 8 37h 27m -
Dwr Cymru Welsh Water Gwalchmai WwTW Storm Overflow Nant Cwyrtai 23 33h 28m -
Dwr Cymru Welsh Water Beaumaris West End Overflow Menai Strait 10 31h 50m -
Dwr Cymru Welsh Water Pont y Brenin Overflow Afon y Brenin 10 30h -
Dwr Cymru Welsh Water Beaumaris Green Overflow Estuarial Waters 11 29h 53m -
Dwr Cymru Welsh Water Beaumaris Green Storm Overflow Menai Strait 10 29h 23m -
Dwr Cymru Welsh Water Unknown Unknown 18 29h 12m -
Dwr Cymru Welsh Water Lon Gardener Valley Overflow Unnamed Watercourse 6 28h -
Dwr Cymru Welsh Water Llansadwrn Anglesy Storm Overflow Afon Cadnant 9 27h 24m -
Dwr Cymru Welsh Water Rhosneigr Overflow Irish Sea 3 27h 17m -
Dwr Cymru Welsh Water Plas Y Ffrwd Rhosybol Storm Overflow River Alaw 5 23h 37m -
Dwr Cymru Welsh Water Rhosneigr Storm Overflow Coastal Waters - Irish Sea 3 17h 47m -
Dwr Cymru Welsh Water Millbank Storm Overflow Unnamed Watercourse 10 16h 9m -
Dwr Cymru Welsh Water Llangefni WwTW Storm Overflow Afon Cefni 24 13h 13m -
Dwr Cymru Welsh Water Malltraeth Overflow Afon Cefni 8 5h 42m -
Dwr Cymru Welsh Water High Street Malltraeth Storm Overflow Afon Cefni 6 5h 12m -
Dwr Cymru Welsh Water Benllech Old Tidal Tanks Storm Overflow Coastal Waters - Benllech 3 4h 54m -
Dwr Cymru Welsh Water Glyn Garth Overflow Menai Strait 5 3h 7m -
Dwr Cymru Welsh Water Llanfair PG Anglesey No 2 Storm Overflow Menai Strait 6 1h 29m -
Dwr Cymru Welsh Water Malltraeth WwTW Inlet Storm Overflow Cefni Estuary 1 1h 13m -
Dwr Cymru Welsh Water Penrhos Beach Holyhead Storm Overflow Beddmanarch Bay 1 1h -
Dwr Cymru Welsh Water Pentraeth Tan Y Graig Storm Overflow River Nodwydd 2 0h 30m -
Dwr Cymru Welsh Water Arosfa Road Dwyran Storm Overflow Afon Braint 1 0h 15m -
Dwr Cymru Welsh Water Llansadwrn Anglesey Storm Overflow Tributary of Afon Cadnant 1 0h 15m -
Dwr Cymru Welsh Water Llanerchymedd WwTW Storm Overflow River Alaw 1 0h 15m -
Dwr Cymru Welsh Water Gorwelion Road Newlands Beach Storm Overflow Estuary Afon Alaw 0 0h -
Dwr Cymru Welsh Water Llyn Y Felin Storm Overflow Menai Strait 0 0h -
Dwr Cymru Welsh Water Unknown Unknown 0 0h -
Dwr Cymru Welsh Water Lon Fain Dwyran Storm Overflow River Braint 0 0h -
Dwr Cymru Welsh Water Llanfaes Overflow Unnamed Watercourse 0 0h -
Dwr Cymru Welsh Water Bae Trearthur Lon Isallt Storm Overflow Adjacent Ditch 0 0h -
Dwr Cymru Welsh Water Unknown Unknown 0 0h -
Dwr Cymru Welsh Water Waterside Holyhead Storm Overflow New Harbour, Holyhead 0 0h -
Dwr Cymru Welsh Water Aberffraw Storm Overflow River Ffraw 0 0h -
Dwr Cymru Welsh Water Llangoed Cynlais Overflow Coastal Waters 0 0h -
Dwr Cymru Welsh Water Gwalchmai Isaf Storm Overflow Unnamed Watercourse 0 0h -
Dwr Cymru Welsh Water Menai Bridge Porth Wrach No 2 Overflow Menai Strait 0 0h -
Dwr Cymru Welsh Water Llyn Y Felin Overflow Menai Strait 0 0h -

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

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.

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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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