List of lakes of Wales

This is a list of lakes in Wales, including those created as reservoirs. The names of most lakes in Wales start with the word "Llyn", which is Welsh for "lake". Except where otherwise referenced, all lakes listed here are named on the relevant Ordnance Survey map at 1:25000 scale.[1]

By area

In terms of surface area, the ten largest lakes in Wales are

All of the above, with the exception of Llyn Tegid, are reservoirs held back by dams. Llyn Tegid was the largest natural lake in Wales though its level has been artificially controlled by sluices since about 1804.[2] The largest natural lake in South Wales is Llangorse Lake (Llyn Syfaddan), which is also the second largest natural lake.

By unitary authority

This list of Welsh lakes ordered by unitary authority includes lakes with a surface area of greater than 5 acres (2.0 ha), but excludes those lakes and ponds created as part of an active industrial site (i.e., works ponds) and also excludes service reservoirs used to store drinking water as part of the water supply system. Grid references identify the approximate centre of the lake or the dam in the case of artificial reservoirs. For some lakes the unitary authority boundary passes through a lake; in these cases the lake is represented in the list for each appropriate authority. Known occurrences include Llyn Brenig, Pontsticill Reservoir, Llwyn-on Reservoir, Cantref Reservoir and Dol-y-gaer Reservoir. All occurrences are marked with an asterisk (*).[3]

Anglesey
Lake name Catchment Grid ref. Area (acres) Status/Use
Llyn Alaw River Alaw SH375853 762 water supply to north Anglesey
Llyn Bodgylched No main catchment SH585770
Llyn Cefni Afon Cefni SH443771 167 water supply to central Anglesey
Llyn Coron No main catchment SH380700 69
Llyn Dinam No main catchment SH312778 24
Llyn y Gors No main catchment SH575748 amenity (fishing)
Llyn Gwaith-glo No main catchment SH450713
Llyn Llygeirian No main catchment SH347898
Llyn Llywenan No main catchment SH347815
Llyn Llwydiarth Afon Braint SH549786
Llyn Maelog No main catchment SH325730 65 former water supply to Rhosneigr
Llyn Pen y Parc No main catchment SH585751 water supply (disused)
Llyn Penrhyn No main catchment SH313770 55 RSPB bird reserve
Llyn Rhosddu No main catchment SH425648
Llyn Traffwll No main catchment SH325770 91
Llyn Treflesg No main catchment SH307770 RSPB bird reserve

Blaenau Gwent
Lake name Catchment Grid ref. Area (acres) Status/Use
Blaen-y-Cwm Reservoir Ebbw River SO174131 50 Reservoir, originally constructed in 1813

to supply the Nantyglo Ironworks.[4]

Carno Reservoir Ebbw River SO164131 reservoir
Cwmtillery Reservoir Ebbw River SO220071 reservoir
Rhyd-y-blew Pond Ebbw River SO160112
Parc Brynbach lake Sirhowy River SO127101 amenity
Shon-Sheffrey's Reservoir Sirhowy River SO129116 reservoir

Bridgend
Lake name Catchment Grid ref. Area (acres) Status/Use
Kenfig Pool River Kenfig SS797815 70 natural lake
Craig yr Aber Reservoir Nant Craig yr Aber SS853857 man-made dam

Caerphilly
Lake name Catchment Grid ref. Area (acres) Status/Use
Lower Blaen Rhymney Reservoir Rhymney River SO103103 reservoir
Upper Blaen Rhymney Reservoir Rhymney River SO098104 reservoir
Bute Town Reservoir Rhymney River SO101091
Caerphilly Castle moat Rhymney River ST155872
Nant-y-draenog Reservoir Sirhowy River ST188935 5 reservoir
Parc Cwm Darran Lake Rhymney River SO117032 amenity
Rhaslas Pond Rhymney River SO095072
Ffrwd Farm lake (west) Rhymney River ST154920 angling
Ffrwd Farm lake (east) Rhymney River ST155920 angling
Pen-y-fan Pond Sirhowy River SO196004 14 built as canal feed reservoir.

Cardiff
Lake name Catchment Grid ref. Area (acres) Status/Use
Cardiff Bay River Taff/River Ely ST190726 500 amenity
Hendre Lake No main catchment ST245805 12 recreation and amenity
Llanishen Reservoir Rhymney River ST185815 59 water supply to Cardiff
Lisvane Reservoir Rhymney River ST189822 water supply to Cardiff
Roath lake Rhymney River ST184795 30 recreation and amenity

Carmarthenshire
Lake name Catchment Grid ref. Area (acres) Status/Use
Llyn Brianne River Tywi SN790485 530 regulation reservoir
Garn Ffrwd pond? Gwendraeth Fach SN508142 5
Llanelli North Dock lake Coastal waterbody SS498996 amenity (former dock)
Llyn Llech Owen Reservoir Gwendraeth Fawr SN568151 amenity/reservoir
Cwm Lliedi Reservoir Afon Lliedi SN519036 ex water supply
Llyn y Fan Fach River Tywi SN803219 25
Llyn Taliaris Afon Dulais SN634283
Lower Talley Lake Afon Cothi SN633331 62 natural lake
Lagoons at National Wetlands Centre Coastal waterbodies SS529986 conservation/wildlife
Old Castle Pond/Pond Twym Coastal lake SN500003 Amenity
Sandy Water Coastal lake SN495003 amenity
Upper Lliedi Reservoir Afon Lliedi SN511045 reservoir
Upper Talley Lake Afon Cothi SN631337 natural lake
Usk Reservoir River Usk SN832288 water supply
Delta Lake Coastal lake SS507987 amenity

Ceredigion
Lake name Catchment Grid ref. Area (acres) Status/Use
Llyn Berwyn River Teifi SN743569 40 natural lake
Llyn Craigypistyll River Dyfi SN722858 natural lake
Dinas Reservoir River Rheidol SN748821 hydroelectricity
Llyn Du River Severn SN800698 natural lake
Llyn Egnant River Teifi SN792674 water supply
Falcondale Lake River Teifi SN569499 amenity
Llyn Frongoch River Ystwyth SN721752 lead mining ?/ natural
Llyn Fyrddon Fach River Severn SN796701 natural lake
Llyn Fyrddon Fawr River Severn SN800708 natural lake
Llyn Glandwgan River Ystwyth SN707752 natural lake
Llyn y Gorlan River Teifi SN786670 water supply
Llyn Gwngi River Severn SN839729 natural lake
Llyn Gynon River Severn SN799647 70 natural lake
Llyn Hir River Teifi SN789676 water supply
Nant-y-moch Reservoir River Rheidol SN751872 hydroelectricity
Llyn Rhosrhydd River Ystwyth SN705759 natural lake
Llyn Syfydrin River Rheidol SN723848 natural lake
Llyn Teifi River Teifi SN781675 water supply

Conwy
Lake name Catchment Grid ref. Area (acres) Status/Use
Aled Isaf Reservoir River Clwyd SH912594 65.7 water supply
Llyn Aled River Clwyd SH917574 112.7 water supply
Llyn Alwen River Dee SH898565 65
Alwen Reservoir River Dee SH943538 372.9 water supply
Llyn Bochlwyd River Ogwen SH654592 10
Llyn Bodgynydd River Conwy SH760592 14 industrial supply (disused)
Llyn Brenig River Dee SH973555 920 flow regulation
Llyn Coedty River Conwy SH754666 11.6 hydroelectricity
Llyn Conwy River Conwy SH780462 101.3 water supply for Llanrwst
Llyn Cowlyd River Conwy SH727624 269 water supply for Conwy
Llyn Crafnant River Conwy SH749610 52 former water supply for Trefriw
Dulyn Reservoir River Conwy SH700665 33 water supply
Llyn Eigiau River Conwy SH720651 120
Llyn Elsi River Conwy SH783552 26 water supply for Betws-y-coed
Llyn Geirionydd River Conwy SH763608 45
Llyn Goddionduon River Conwy SH753586 10
Ffynnon Lloer River Ogwen SH662621 6
Ffynnon Llugwy River Conwy SH692627 40
Llynnau Mymbyr River Conwy SH708575 58
Llyn Ogwen River Ogwen SH659604 78
Llyn y Parc River Conwy SH792588 22
Llyn-y-foel Afon Lledr SH714547 natural lake

Denbighshire
Lake name Catchment Grid ref. Area (acres) Status/Use
Brickfields Pond River Clwyd SJ012803 8.9 Local nature reserve
Llyn Brân SH961592 31.4
Llyn Brenig River Dee SH973555 920 flow regulation
Llyn Cyfynwy SJ217546 17.5
Llyn Gweryd SJ172550 13.1
Llyn Mynyllod SJ012402 6.2
Nant-y-Ffrith Reservoir River Cegidog SJ242530 12.1
Pendinas Reservoir River Cegidog SJ235518 16.3
Rhyl Marine Lake River Clwyd SH999804 28.7
unnamed lake on Rûg estate River Dee SJ058440 8.4

Flintshire
Lake name Catchment Grid ref. Area (acres) Status/Use
Llyn Helyg River Clwyd SJ113772 37
Padeswood Pool SJ278619 12.6 angling
Shotwick Lake River Dee SJ315725 amenity
unnamed reservoir, Cilcain SJ155641 5.4
unnamed reservoir, Oakenholt SJ262710 5.7
Ysceifiog Lake SJ147716 13.8

Gwynedd
Lake name Catchment Grid ref. Area (acres) Status/Use
Llyn yr Adar River Glaslyn SH655479 10
Llyn Anafon Afon Aber SH698698 13 water supply
Llyn Arenig Fach SH827417 34 natural lake
Llyn Arenig Fawr River Dee SH846380 84 water supply for Bala town, natural lake
Llynnau Barlwyd River Dwyryd SH710484 10 + 5 industrial water supply
Llyn y Bi River Mawddach SH669264 6
Llyn Bodlyn Afon Ysgethin SH648239 42 water supply
Llyn Bowydd River Dwyryd SH725467 22 industrial water supply.
Llyn Caerwych River Dwyryd SH640350 5
Llyn Cau River Dysynni SH714123 33
Llyn Celyn River Dee SH860405 815 river regulation
Llyn Conglog River Dwyryd SH674473 18
Llyn Conglog Mawr River Dwyryd SH758387 8
Craiglyn Dyfi also written as Creiglyn Dyfi River Dyfi SH867225 15 natural corrie lake
Llyn Croesor River Glaslyn SH661457 5
Llyn Cwm Corsiog Afon Dwyryd SH663470 7 industrial water supply (disused)
Llyn Cwellyn Afon Gwyrfai SH559549 215 water supply
Llyn Cwm Bychan Afon Artro SH640312 25
Llyn Cwm Dulyn Afon Llyfni SH492495 34 water supply
Llyn Cwmffynnon River Conwy SH649562 20
Llyn Cwm-mynach River Mawddach SH678237 14
Llyn Cwmorthin River Dwyryd SH677463 22
Llynnau Cwm Silyn Afon Llyfni SH513508 15 + 15
Llyn Cwm y Foel River Glaslyn SH655468 8
Llyn Cwmystradllyn River Dwyfor SH561444 98 natural lake
Llyn Cynwch River Mawddach SH737207 26 amenity
Llyn Dinas River Glaslyn SH616495 60 natural lake
Llynnau Diwaunedd River Conwy SH682537 19 + 13 natural lakes
Llyn Dulyn Afon Ysgethin SH661244 5 natural lake, reservoir
Llyn Du'r Arddu River Seiont SH600557 5 natural lake
Llyn Dwythwch River Seiont SH570580 24
Llyn y Dywarchen Afon Gwyrfai SH560534 40
Llyn Edno River Glaslyn SH663497 10
Llyn Eiddew-mawr Afon Artro SH646338 22
Llyn Ffynnon y Gwas Afon Gwyrfai SH591553 10
Llyn y Gadair Afon Gwyrfai SH568521 50
Llyn Gwynant River Glaslyn SH644519 85
Llyn Hesgyn River Dee SH885442 5
Llyn Hywel SH663266 13
Llyn Idwal River Ogwen SH645596 28
Llyn Irddyn Afon Ysgethin SH629222 natural lake
Llyn Llagi River Glaslyn SH649482 8
Llyn Llydaw River Glaslyn SH629543 110
Llyn Llywelyn River Glaslyn SH562499 6
Llyn Mair River Dwyryd SH652412 14
Llyn Manod River Dwyryd SH717449 16[5]
Marchlyn Bach reservoir River Seiont SH607625
Marchlyn Mawr River Seiont SH615622 hydroelectricity
Llyn Mwyngil (Talyllyn Lake) River Dysynni SH717099 220
Llyn Nantlle Uchaf Afon Llyfni SH514530 80
Llyn Newydd River Dwyryd SH722471 12
Llyn Peris River Seiont SH591595 95 lower reservoir for pump storage hydro-electricity
Llyn Padarn River Seiont SH572613 280 natural lake used for recreation
Tanygrisiau Reservoir River Dwyryd SH679441 95
Llyn Tecwyn Isaf SH629370 7
Llyn Tecwyn Uchaf River Dwyryd SH640381 31
Llyn Tegid (Bala Lake) River Dee SH911338 1,196
Llyn Teyrn River Glaslyn SH641547 5
Llyn Trawsfynydd River Dwyryd SH674377 1,180 nuclear power (formerly) and hydroelectric energy
Llyn Tryweryn River Dee SH788384 20
Llyn Wylfa Afon Mawddach SH671162 6 natural lake

Merthyr Tydfil
Lake name Catchment Grid ref. Area (acres) Status/Use
Cyfarthfa Castle Lake River Taff SO039073 amenity
Dol-y-gaer (or Pentwyn) Reservoir * River Taff SO060118 water supply
Llwyn-on Reservoir * River Taff SO012113 water supply
Penywern Middle Pond River Taff SO073083 angling
Penywern Top Pond River Taff SO071086 angling
Pontsticill Reservoir * River Taff SO060118 water supply

Monmouthshire
Lake name Catchment Grid ref. Area (acres) Status/Use
Llandegfedd Reservoir River Usk ST325985 434 water supply
Pwll Pen-ffordd-goch / Keepers Pond River Usk SO255109 amenity, formerly served Garn-ddyrys ironworks
Wentwood Reservoir River Usk ST430929 41 water supply

Neath Port Talbot
Lake name Catchment Grid ref. Area (acres) Status/Use
Cwmwernderi Reservoir SS817902 reservoir
Eglwys Nunydd River Afan SS791855 260 industrial water supply, fishing
Furzemill Pond River Afan SS810857 5 former millpond?
Rheola Pond River Neath SN843043
larger un-named lake at Aberclwyd River Neath SN847043 amenity
smaller un-named lake at Aberclwyd River Neath SN852045 amenity

Pembrokeshire
Lake name Catchment Grid ref. Area (acres) Status/Use
Bosherston lakes Coastal stream SR974946 natural lakes
Llys-y-Frân Reservoir Western Cleddau SN036242 212 water supply
Rosebush Reservoir Western Cleddau SN061291 30 water supply

Powys
Lake name Catchment Grid ref. Area (acres) Status/Use
Abernant Lake River Irfon SN891462 5 Created in 1903 by damming an oxbow of the Irfon
Beacons Reservoir River Taff SN987182 52 water supply
Bugeilyn River Dyfi SN822923
Caban-coch Reservoir River Severn SN924645 500See note water supply
Cantref Reservoir * River Taff SN996154 42 water supply
Claerwen Reservoir River Severn SN854651 664 water supply
Llyn Clywedog River Severn SN911870 river regulation
Craig-goch Reservoir River Severn SN893686 217 water supply
Cray Reservoir River Usk SN883220 100 water supply
Dol-y-gaer (or Pentwyn) Reservoir * River Taff SO054144 water supply
Garreg-ddu Reservoir River Severn SN911639 500See note water supply
Llyn Glanmerin River Dyfi SN755990 natural lake
Glaslyn River Dyfi SN826941
Llyn Gludy River Usk SO018298
Llangorse Lake River Usk SO132266 327 natural lake
Llangynidr Reservoir Ebbw River SO153141 reservoir
Llyn Lluncaws Afon Tanat SJ07143169 natural lake
Llyn y Fan Fawr River Tawe SN832216
Lower Neuadd Reservoir River Taff SO030180 water supply
Upper Neuadd Reservoir River Taff SO029188 water supply
Penygarreg Reservoir River Severn SN911673 124 water supply
Pontsticill Reservoir* River Taff SO060118 water supply
Pwll Gwy-rhoc River Clydach SO183153 c.5 natural lake
Talybont Reservoir River Usk SO104205 water supply
Ty Mawr Pool River Usk SO074264 natural lake
Lake Vyrnwy River Vyrnwy SH989213 water supply
Ystradfellte Reservoir River Neath SN945175 water supply

Note: Caban Coch and Garreg-ddu reservoirs are separately named but form one contiguous area of water at normal levels. The area quoted is for the two combined. At high water levels, Pentwyn Reservoir is continuous with Pontsticill Reservoir, its dam being submerged.

Rhondda Cynon Taf
Lake name Catchment Grid ref. Area (acres) Status/Use
Cantref Reservoir * River Taff SN996154 water supply
Dare Valley Country Park lower lake River Cynon SN977028 amenity
Lluest-wen Reservoir River Rhondda Fach SN947017
Llwyn-on Reservoir * River Taff SO012113 150 water supply
Llyn Fawr River Cynon SN917034 24
Nant-hir Reservoir River Cynon SN989069
Nant-moel Reservoir River Cynon SN982071
Penderyn Reservoir River Neath SN938072
?Perthgelyn Reservoir River Cynon ST053970 reservoir

Swansea
Lake name Catchment Grid ref. Area (acres) Status/Use
Lake Fendrod River Tawe SS676967 13 amenity
Lower Lliw Reservoir River Lliw SN650036 water supply
Oxwich Marsh Lake coastal stream SS503873 >15 natural lake
Upper Lliw Reservoir River Lliw SN661062 water supply
Tawe Barrage River Tawe SS664926 amenity
Specimen Lake River Loughor SN598056 10 amenity/angling

Torfaen
Lake name Catchment Grid ref. Area (acres) Status/Use
Blaen Bran Reservoir (lower) Afon Lwyd ST267971
Coity Pond Afon Lwyd SO233090 former reservoir

Vale of Glamorgan
Lake name Catchment Grid ref. Area (acres) Status/Use
Cosmeston Lake River Cadoxton ST176692 amenity
Hensol Lake River Ely ST045789 amenity and reservoir
Hensol Mill Pond River Ely ST050790 6 former mill pond

Wrexham
Lake name Catchment Grid ref. Area (acres) Status/Use
Cae Llwyd Reservoir SJ270479 10.6
Chirk Castle Lake SJ269386 11.1
Fenn's Bank Mere SJ505386 8.4
Gresford Flash SJ346536 8.2 amenity
Hanmer Mere SJ452392 45.2 natural lake
Monk's Pool SJ303448 5.2
Pant-yr-ochain Lake SJ349529 14.1
Penycae Top Reservoir SJ267452 6.2
Ty Mawr Reservoir SJ276480 21.3
Wynnstay Park Lake SJ307428 8.9

By national park

Lakes and reservoirs within each of Wales' three national parks.

Brecon Beacons
Lake name Catchment Grid ref. Area (acres) Status/Use Unitary area/s
Beacons Reservoir River Taff SN987182 52 water supply Powys
Cantref Reservoir * River Taff SN996154 42 water supply Powys, Rhondda Cynon Taf
Cray Reservoir River Usk SN883220 100 water supply Powys
Dol-y-gaer (or Pentwyn) Reservoir * River Taff SO054144 water supply Powys
Llyn Gludy River Usk SO018298 Powys
Llangorse Lake River Wye SO132266 327 natural lake Powys
Llangynidr Reservoir Ebbw River SO153141 reservoir Powys
Llwyn-on Reservoir * River Taff SO012113 150 water supply Merthyr Tydfil, Rhondda Cynon Taf
Llyn y Fan Fawr River Tawe SN832216 natural lake Powys
Lower Neuadd Reservoir River Taff SO030180 water supply Powys
Upper Neuadd Reservoir River Taff SO029188 water supply Powys
Pontsticill Reservoir* River Taff SO060118 water supply Merthyr Tydfil, Powys
Pwll Gwy-rhoc River Clydach SO183153 c.5 natural lake Powys
Talybont Reservoir River Usk SO104205 water supply Powys
Ty Mawr Pool River Usk SO074264 natural lake Powys
Ystradfellte Reservoir River Neath SN945175 water supply Powys

Pembrokeshire Coast
Lake name Catchment Grid ref. Area (acres) Status/Use Unitary area/s
Bosherston lakes Coastal stream SR974946 natural lakes Pembrokeshire
Rosebush Reservoir, Rosebush Western Cleddau SN061291 30 water supply Pembrokeshire

Snowdonia
Lake name Catchment Grid ref. Area (acres) Status/Use unitary area/s
Llyn yr Adar River Glaslyn SH655479 10 Gwynedd
Llyn Anafon Afon Aber SH698698 13 water supply
Llyn Arenig Fach SH827417 34 natural lake Gwynedd
Llyn Arenig Fawr River Dee SH846380 84 water supply, natural lake Gwynedd
Llynnau Barlwyd River Dwyryd SH710484 10 + 5 industrial water supply Gwynedd
Llyn y Bi River Mawddach SH669264 6 Gwynedd
Llyn Bochlwyd River Ogwen SH654592 10 Conwy
Llyn Bodgynydd SH760592 14 industrial supply (disused) Conwy
Llyn Bodlyn Afon Ysgethin SH648239 42 water supply Gwynedd
Llyn Bowydd River Dwyryd SH725467 22 industrial water supply Gwynedd
Llyn Caerwych River Dwyryd SH640350 5 Gwynedd
Llyn Cau River Dysynni SH714123 33 Gwynedd
Llyn Celyn River Dee SH858405 815 river regulation Gwynedd
Llyn Coedty River Conwy SH754666 11.6 hydroelectricity Conwy
Llyn Conglog River Dwyryd SH674473 18 Gwynedd
Llyn Conglog Mawr River Dwyryd SH758387 8 Gwynedd
Llyn Conwy River Conwy SH780462 101.3 water supply for Llanrwst Conwy
Llyn Cowlyd River Conwy SH727624 269 water supply for Conwy Conwy
Llyn Crafnant River Conwy SH749610 52 former water supply Conwy
Creiglyn Dyfi River Dyfi SH867225 15 natural corrie lake Gwynedd
Llyn Croesor River Glaslyn SH661457 5 Gwynedd
Llyn Cwm Corsiog SH663470 7 industrial water supply (disused)
Llyn Cwellyn Afon Gwyrfai SH559549 215 water supply Gwynedd
Llyn Cwm Bychan Afon Artro SH640312 25 Gwynedd
Llyn Cwm Dulyn Afon Llyfni SH492495 34 water supply Gwynedd
Llyn Cwmffynnon River Conwy SH649562 20 Gwynedd
Llyn Cwm-mynach River Mawddach SH678237 14 Gwynedd
Llyn Cwmorthin River Dwyryd SH677463 22 Gwynedd
Llynnau Cwm Silyn Afon Llyfni SH513508 15 + 15 Gwynedd
Llyn Cwm y Foel River Glaslyn SH655468 8 Gwynedd
Llyn Cwmystradllyn River Dwyfor SH561444 98 natural lake Gwynedd
Llyn Cynwch River Mawddach SH737207 26 amenity Gwynedd
Llyn Dinas River Glaslyn SH616495 60 natural lake Gwynedd
Llynnau Diwaunedd River Conwy SH682537 19 + 13 natural lakes Gwynedd
Llyn Dulyn Afon Ysgethin SH661244 5 natural lake, reservoir Gwynedd
Dulyn Reservoir River Conwy SH700665 33 water supply Conwy
Llyn Du'r Arddu River Seiont SH600557 5 natural lake Gwynedd
Llyn Dwythwch River Seiont SH570580 24 Gwynedd
Llyn y Dywarchen Afon Gwyrfai SH560534 40 Gwynedd
Llyn Edno River Glaslyn SH663497 10 Gwynedd
Llyn Eiddew-mawr Afon Artro SH646338 22 Gwynedd
Llyn Eigiau River Conwy SH720651 120 Conwy
Llyn Elsi River Conwy SH783552 26 water supply Conwy
Llyn Ffynnon y Gwas Afon Gwyrfai SH591553 10 Gwynedd
Llyn-y-foel Afon Lledr SH714547 natural lake Conwy
Llyn y Gadair Afon Gwyrfai SH568521 50 Gwynedd
Llyn Geirionydd River Conwy SH763608 45 Conwy
Llyn Goddionduon River Conwy SH753586 10 Conwy
Llyn Gwynant River Glaslyn SH644519 85 Gwynedd
Llyn Hesgyn River Dee SH885442 5 Gwynedd
Llyn Hywel SH663266 13 Gwynedd
Llyn Idwal River Ogwen SH645596 28 Gwynedd
Llyn Irddyn Afon Ysgethin SH629222 natural lake Gwynedd
Llyn Llagi River Glaslyn SH649482 8 Gwynedd
Ffynnon Lloer River Ogwen SH662621 6 Conwy
Ffynnon Llugwy River Conwy SH692627 40 Conwy
Llyn Llydaw River Glaslyn SH629543 110 Gwynedd
Llyn Llywelyn River Glaslyn SH562499 6 Gwynedd
Llyn Mair River Dwyryd SH652412 14 Gwynedd
Marchlyn Bach reservoir River Seiont SH607625 Gwynedd
Marchlyn Mawr River Seiont SH615622 hydroelectricity Gwynedd
Llyn Mwyngil (Talyllyn Lake) River Dysynni SH717099 220 Gwynedd
Llynnau Mymbyr River Conwy SH708575 58 Conwy
Llyn Nantlle Uchaf Afon Llyfni SH514530 80 Gwynedd
Llyn Newydd River Dwyryd SH722471 12 Gwynedd
Llyn Ogwen River Ogwen SH659604 78 Conwy
Llyn y Parc River Conwy SH792588 22 Conwy
Tanygrisiau Reservoir River Dwyryd SH679441 95 Gwynedd
Llyn Tecwyn Isaf SH629370 7 Gwynedd
Llyn Tecwyn Uchaf River Dwyryd SH640381 31 Gwynedd
Llyn Tegid – (Bala Lake) River Dee SH911338 1,196 Gwynedd
Llyn Teyrn River Glaslyn SH641547 5 Gwynedd
Llyn Trawsfynydd River Dwyryd SH674377 1,180 nuclear power (formerly) & HEP Gwynedd
Llyn Tryweryn River Dee SH788384 20 Gwynedd
Llyn Wylfa SH671163 6 Gwynedd

By supply to England

Most Welsh lakes supply the nation itself with water, however, there are lakes and reservoirs which supply England.[6][7]

The main reservoirs created for this purpose include:

Reservoir name Location Built by Supplies water to
Lake Vyrnwy Powys Liverpool Corporation Liverpool, Cheshire and Manchester
Claerwen Elan Valley reservoirs Birmingham Corporation Water Department Birmingham
Craig-goch Elan Valley reservoirs Birmingham Corporation Water Department Birmingham
Pen-y-garreg Elan Valley reservoirs Birmingham Corporation Water Department Birmingham
Garreg-ddu Elan Valley reservoirs Birmingham Corporation Water Department Birmingham,
Caban-coch[8] Elan Valley reservoirs Birmingham Corporation Water Department Birmingham
Alwen Reservoir Conwy The Corporation of Birkenhead Birkenhead[9]
Llyn Celyn (via and Bala Lake) Gwynedd Liverpool Corporation Waterworks Liverpool
Llyn Clywedog Powys Reed and Mallick of Salisbury Shropshire, West Midlands to Bristol


Former lakes
Lake name Catchment Grid ref. Area (acres) Status/Use Unitary area
Bryn-bach Pond[10] Sirhowy River SO122100 formerly industrial use (not same site as modern lake) Blaenau Gwent
Cairn Mound Impounding Reservoir River Clydach SO202136 former reservoir[11] Blaenau Gwent
Clyn-mil Pond[12] River Taff SO062052 formerly industrial use Merthyr Tydfil
Glyn-dyrys Pond[13] River Taff SO049047 formerly industrial use Merthyr Tydfil
Hirwaun Ponds[14] River Cynon SN945060 formerly industrial use Rhondda Cynon Taf
Lower Neuadd Reservoir River Taff SO030180 former reservoir (dam breached) Merthyr Tydfil[15]
Llyn Nantlle-isaf[16] Afon Llyfni SH506528 natural lake Gwynedd
Pitwellt Pond River Taff SO078098 former reservoir (dam breached) Merthyr Tydfil
Rhyd-y-blew Pond (Rassa) Ebbw River SO160112 formerly industrial use Blaenau Gwent
Scotch Peter's Reservoir[17] Sirhowy River SO155088 former reservoir Blaenau Gwent

References
  1. Ordnance Survey maps. 1:25000
  2. "Bala Bridge Sluice Gates". Royal Commission on the Ancient and Historical Monuments of Wales. 24 March 2010. Retrieved 2 September 2020.
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