Wales
 | This section needs to be updated. The reason given is: Some may be under the incorrect heading.(May 2022) |
Anglesey
- Llyn Alaw - water supply to much of north Anglesey
- Llyn Cefni - water supply to central Anglesey
Bridgend
- Kenfig Pool - Natural Lake [6]
Cardiff
- Llanishen Reservoir - water supply to Cardiff
- Lisvane Reservoir - water Supply to Cardiff
Carmarthenshire
- Upper and Lower Cwm Lliedi reservoirs also known as Swiss Valley reservoirs [7] [8]
- Llyn Brianne
- Llyn y Fan Fach
- Usk Reservoir
Ceredigion
Conwy
- Llyn Bodgynydd - supply for the Pandora lead mine (disused)
- Llyn Brenig - part of Dee Regulation system - also in Denbighshire
- Llyn Coedty - water supply for Dolgarrog hydroelectric station
- Llyn Conwy - water supply for Llanrwst and Betws-y-Coed
- Llyn Cowlyd - water supply for Conwy and Colwyn Bay and for Dolgarrog hydroelectric station
- Llyn Crafnant - water supply for Llanrwst
- Llyn Dulyn - water supply for Llandudno
- Llyn Melynllyn - water supply for Llandudno
- Llyn Parc - supply for the Aberllyn mine (disused)
- Llyn Elsi - water supply for Betws-y-Coed (disused)
Denbighshire
- Aled Isaf Reservoir
- Alwen Reservoir
- Llyn Aled
- Llyn Alwen
- Llyn Brenig - part of the River Dee regulation system
- Llyn Celyn - part of the River Dee regulation system.
- Pendinas Reservoir
- Bala Lake (Llyn Tegid)
- Nant-y-Ffrith Reservoir
Gwynedd
- Llyn Anafon - water supply for Llanfairfechan, Dwygyfylchi and Penmaenmawr
- Llyn Arenig Fach
- Llyn Arenig Fawr - water supply for Bala town
- Llynnau Barlwyd - supply to Llechwedd slate quarry
- Llyn Bodlyn - water supply to Barmouth.
- Llyn Bowydd - supply to the Blaenau Ffestiniog slate quarries
- Llyn Cwm Corsiog - supply for Rhosydd slate quarry (disused)
- Llyn Cwellyn - water supply to Bangor and parts of south Anglesey
- Marchlyn Mawr - header reservoir for the Dinorwig power station hydroelectric system.
- Llyn Peris
- Llyn Padarn - part of the Dinorwig hydroelectric system
- Llyn Stwlan - built for the hydroelectric Ffestiniog Power Station
- Llyn Trawsfynydd - built for the Maentwrog hydroelectric Power Station
Merthyr Tydfil
- Llwyn-on Reservoir
- Pontsticill Reservoir, including Pentwyn Reservoir
Neath Port Talbot
- Eglwys Nunydd - water supply to Tata Steel Europe steel-works at Port Talbot
Pembrokeshire
- Bosherston Lakes - artificial amenity lakes
- Llys-y-Frân Reservoir
- Rosebush Reservoir
Powys
- Taff Fawr reservoirs- a chain of three reservoirs supplying the Rhondda and Taff valley and Cardiff with water
- Beacons Reservoir
- Cantref Reservoir
- also see Llwyn-on Reservoir in Merthyr Tydfil
- Taff Fechan reservoirs - a chain of four reservoirs also supplying the Taff valley and Cardiff with water
- Elan Valley Reservoirs - a group of reservoirs supplying Birmingham and parts of the West Midlands conurbation with drinking water
- Lake Vyrnwy (Llyn Efyrnwy) - supplies water to the Liverpool area
- Talybont Reservoir
- Ystradfellte Reservoir
- Clywedog Reservoir (Llyn Clywedog)
Rhondda Cynon Taf
Swansea
- Cray Reservoir
- Swansea Barrage
- Upper and Lower Lliw Reservoirs
