Top of the Poops | Constituency Sewage Map

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View Annual Sewage Data

You're looking at the totals that we have calculated for sewage in Ynys Môn so far for 2026. It is an estimate, based on very poor quality live data from the Water Companies. The water companies report their sewage to the Environment Agency every year in April. You can see the last reported year in the other page

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.

Totals for Ynys Môn in 2026

Sewage12,020 hours

Monitoring offline0 hours

Potential pollution0 hours

Storm overflows97

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Your local MP is Llinos Medi (Plaid Cymru) - Find out more about their interests, donors, and voting at They Work For You

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Company	Site Name	Receiving Waterway	Overflow Days	Total Duration (hours)	Offline/Potential Pollution
Dwr Cymru Welsh Water	Llanfachraeth WwTW Overflow	River Alaw	177	2,946h 5m	-
Dwr Cymru Welsh Water	Bryngwran WwTW Overflow	Crigyll	144	1,934h 51m	-
Dwr Cymru Welsh Water	Llangaffo WwTW Storm Overflow	Unnamed Stream	173	1,067h 17m	-
Dwr Cymru Welsh Water	Talwrn Llangefni Storm Overflow	Unnamed Ditch	40	617h 29m	-
Dwr Cymru Welsh Water	Brynsiencyn WwTW Storm Overflow	Menai Strait	99	601h 55m	-
Dwr Cymru Welsh Water	Craig Y Don Storm Overflow	Afon Goch	63	596h 19m	-
Dwr Cymru Welsh Water	Green Terrace Llangaffo Storm Overflow	Unnamed Ditch	34	561h 41m	-
Dwr Cymru Welsh Water	Llandegfan Menai Bridge Storm Overflow	Afon Cadnant	31	423h 26m	-
Dwr Cymru Welsh Water	Menai Llandegfan Storm Overflow	Menai Strait	24	332h 48m	-
Dwr Cymru Welsh Water	Llanfechell WwTW Storm Overflow	Afon Meddanen	30	301h 25m	-
Dwr Cymru Welsh Water	Llaneilian Storm Overflow	Coastal Waters	22	289h 31m	-
Dwr Cymru Welsh Water	Bull Bay Storm Overflow	Bull Bay	39	211h 45m	-
Dwr Cymru Welsh Water	Train Station Gaerwen Storm Overflow	Tributary of Afon Braint	18	185h 29m	-
Dwr Cymru Welsh Water	Lon Sardis Bodffordd Storm Overflow	Cefni Reservoir Bypass Channel	33	166h 46m	-
Dwr Cymru Welsh Water	Llanfair Pwllgwyngyll WwTW Storm Overflow	Menai Strait	64	153h 12m	-
Dwr Cymru Welsh Water	Hermon Malltraeth Storm Overflow	Afon Frechwen	9	139h 30m	-
Dwr Cymru Welsh Water	London Road Valley Storm Overflow	Unnamed Watercourse	21	123h 16m	-
Dwr Cymru Welsh Water	Rhosybol Gorslwyd Storm Overflow	Unnamed Watercourse	38	121h 59m	-
Dwr Cymru Welsh Water	Aberffraw WwTW Storm Overflow	Aberffraw Bay	9	99h 20m	-
Dwr Cymru Welsh Water	Holyhead Porth Y Felin Storm Overflow	Unnamed Ditch draining to New Harbour	14	93h 29m	-
Dwr Cymru Welsh Water	Gorsllwyd Llanddona Storm Overflow	Afon Cadnant	13	85h 42m	-
Dwr Cymru Welsh Water	Star Gaerwen Storm Overflow	Afon Braint	11	74h	-
Dwr Cymru Welsh Water	Copperfield Close Four Mile Bridge Storm Overflow	Holy Island Straits South	7	65h 45m	-
Dwr Cymru Welsh Water	Waterside Holyhead Storm Overflow	New Harbour, Holyhead	33	65h 44m	-
Dwr Cymru Welsh Water	Beaumaris & Llanfaes WwTW Storm Overflow	Menai Strait	20	55h 25m	-
Dwr Cymru Welsh Water	Llanfaelog Storm Overflow	Llyn Maelog	6	54h 28m	-
Dwr Cymru Welsh Water	Menai Bridge Faelog Causeway 1 Overflow	Menai Strait	27	53h 43m	-
Dwr Cymru Welsh Water	Menai Ville Storm Overflow	Menai Strait	27	53h 43m	-
Dwr Cymru Welsh Water	Benllech WwTW Storm Overflow	Coastal Waters - Benllech	24	53h 42m	-
Dwr Cymru Welsh Water	Pont Y Crug Llanddaniel Storm Overflow	Afon Braint	16	50h 26m	-
Dwr Cymru Welsh Water	Menai Suspension Bridge No 3 Overflow	Menai Strait	27	48h 29m	-
Dwr Cymru Welsh Water	Menai Bridge Suspension Storm Overflow	Menai Strait	27	48h 15m	-
Dwr Cymru Welsh Water	Lon Fain Dwyran Storm Overflow	River Braint	6	45h 41m	-
Dwr Cymru Welsh Water	Gorad Beach Road Storm Overflow	Estuarial Waters of Afon Alaw	9	40h 57m	-
Dwr Cymru Welsh Water	Holyhead Turkey Shore Storm Overflow	Old Harbour Holyhead	18	33h 20m	-
Dwr Cymru Welsh Water	Fford Cae Sel Storm Overflow	Drainage Ditch	7	26h 2m	-
Dwr Cymru Welsh Water	Prince of Wales Road Storm Overflow	New Harbour, Holyhead	30	25h 58m	-
Dwr Cymru Welsh Water	Newborough WwTW Storm Overflow	Afon Braint	10	24h 53m	-
Dwr Cymru Welsh Water	London Road Valley no.2 Storm Overflow	Unname Watercourse	13	23h 46m	-
Dwr Cymru Welsh Water	Afon Goch Lon Parys Amlwch Storm Overflow	Afon Goch	10	21h 2m	-
Dwr Cymru Welsh Water	Llangoed Lleiniog Overflow	Menai Strait	5	13h 12m	-
Dwr Cymru Welsh Water	Lon Sardis Storm Overflow	River Cefni	12	13h 4m	-
Dwr Cymru Welsh Water	Holyhead Bae Trearthur No1 Storm Overflow	Estuarial Waters of the Inland Sea	10	11h 58m	-
Dwr Cymru Welsh Water	Fryars Bay Llanfaes Overflow	Menai Strait	8	9h 1m	-
Dwr Cymru Welsh Water	Rhosneigr Overflow	Irish Sea	1	5h 15m	-
Dwr Cymru Welsh Water	Ffordd Y Traeth Cemaes Bay Storm Overflow	Cemaes Bay	2	4h 29m	-
Dwr Cymru Welsh Water	Plas Y Ffrwd Rhosybol Storm Overflow	River Alaw	2	4h 28m	-
Dwr Cymru Welsh Water	Beaumaris West End Overflow	Menai Strait	6	3h 59m	-
Dwr Cymru Welsh Water	Llyn Y Felin Storm Overflow	Menai Strait	3	3h 30m	-
Dwr Cymru Welsh Water	Llyn Y Felin Overflow	Menai Strait	3	3h 30m	-
Dwr Cymru Welsh Water	Beaumaris Green Overflow	Estuarial Waters	4	3h 14m	-
Dwr Cymru Welsh Water	Llandegfan Rhianfa Overflow	Menai Strait	4	2h 45m	-
Dwr Cymru Welsh Water	Moelfre Car Park Storm Overflow	Coastal Waters of the Irish Sea	1	2h 45m	-
Dwr Cymru Welsh Water	Holyhead WwTW Overflow	Unnamed Watercourse	3	2h 44m	-
Dwr Cymru Welsh Water	Holyhead Morawelon Storm Overflow	Outer Harbour, Holyhead	9	2h 34m	-
Dwr Cymru Welsh Water	Gwalchmai WwTW Storm Overflow	Nant Cwyrtai	3	2h 17m	-
Dwr Cymru Welsh Water	Bae Trearthur Isallt Bach Overflow	Caernarfon Bay North	2	1h 59m	-
Dwr Cymru Welsh Water	Cycle Way Llangefni Storm Overflow	Afon Cefni	5	1h 57m	-
Dwr Cymru Welsh Water	Rhosneigr Storm Overflow	Coastal Waters - Irish Sea	1	1h 45m	-
Dwr Cymru Welsh Water	Bodedern Main Storm Overflow	River Alaw	3	1h 30m	-
Dwr Cymru Welsh Water	Pont y Brenin Overflow	Afon y Brenin	3	1h 29m	-
Dwr Cymru Welsh Water	Glyn Garth Overflow	Menai Strait	2	1h 11m	-
Dwr Cymru Welsh Water	Malltraeth WwTW Inlet Storm Overflow	Cefni Estuary	1	1h 2m	-
Dwr Cymru Welsh Water	Holyhead Hibernia Row Storm Overflow	New Harbour, Holyhead	1	0h 30m	-
Dwr Cymru Welsh Water	Millbank Storm Overflow	Unnamed Watercourse	1	0h 30m	-
Dwr Cymru Welsh Water	Holyhead Bae Trearthur No2 Storm Overflow	Unnamed Watercourse	1	0h 27m	-
Dwr Cymru Welsh Water	Lon Gardener Valley Overflow	Unnamed Watercourse	1	0h 15m	-
Dwr Cymru Welsh Water	Malltraeth WwTW Storm Overflow	Cefni Estuary	1	0h 15m	-
Dwr Cymru Welsh Water	Gorwelion Road Newlands Beach Storm Overflow	Estuary Afon Alaw	0	0h	-
Dwr Cymru Welsh Water	Arosfa Road Dwyran Storm Overflow	Afon Braint	0	0h	-
Dwr Cymru Welsh Water	Unknown	Unknown	0	0h	-
Dwr Cymru Welsh Water	Brynsciencyn Overflow	Menai Strait	0	0h	-
Dwr Cymru Welsh Water	Pentraeth Tan Y Graig Storm Overflow	River Nodwydd	0	0h	-
Dwr Cymru Welsh Water	Llansadwrn Anglesey Storm Overflow	Tributary of Afon Cadnant	0	0h	-
Dwr Cymru Welsh Water	Llanfaes Overflow	Unnamed Watercourse	0	0h	-
Dwr Cymru Welsh Water	High Street Malltraeth Storm Overflow	Afon Cefni	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	Llangefni Main Storm Overflow	Afon Cefni	0	0h	-
Dwr Cymru Welsh Water	Aberffraw Storm Overflow	River Ffraw	0	0h	-
Dwr Cymru Welsh Water	Malltraeth Overflow	Afon Cefni	0	0h	-
Dwr Cymru Welsh Water	Llansadwrn Anglesy Storm Overflow	Afon Cadnant	0	0h	-
Dwr Cymru Welsh Water	Brynsiencyn Main Storm Overflow	Menai Strait	0	0h	-
Dwr Cymru Welsh Water	Beaumaris Green Storm Overflow	Menai Strait	0	0h	-
Dwr Cymru Welsh Water	Penrhos Beach Holyhead Storm Overflow	Beddmanarch Bay	0	0h	-
Dwr Cymru Welsh Water	Llanfair PG Anglesey No 2 Storm Overflow	Menai Strait	0	0h	-
Dwr Cymru Welsh Water	Llangoed Cynlais Overflow	Coastal Waters	0	0h	-
Dwr Cymru Welsh Water	Llanerchymedd WwTW Storm Overflow	River Alaw	0	0h	-
Dwr Cymru Welsh Water	Unknown	Unknown	0	0h	-
Dwr Cymru Welsh Water	Gwalchmai Isaf Storm Overflow	Unnamed Watercourse	0	0h	-
Dwr Cymru Welsh Water	Gaerwen WwTW Storm Overflow	Afon Cefni	0	0h	-
Dwr Cymru Welsh Water	Llangefni WwTW Storm Overflow	Afon Cefni	0	0h	-
Dwr Cymru Welsh Water	Menai Bridge Porth Wrach No 2 Overflow	Menai Strait	0	0h	-
Dwr Cymru Welsh Water	Unknown	Unknown	0	0h	-
Dwr Cymru Welsh Water	Amlwch Port Storm Overflow	Coastal Waters - Amlwch Harbour	0	0h	-
Dwr Cymru Welsh Water	Unknown	Unknown	0	0h	-
Dwr Cymru Welsh Water	Benllech Old Tidal Tanks Storm Overflow	Coastal Waters - Benllech	0	0h	-

Ynys Môn - Live Sewage

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