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.

By area
In terms of surface area, the ten largest lakes in Wales are
 * Bala Lake (Llyn Tegid) — 1196 acre
 * Llyn Trawsfynydd — 1180 acre
 * Lake Vyrnwy — 1120 acre
 * Llyn Brenig — 894 acre
 * Llyn Celyn — 800 acre
 * Llyn Alaw — 762 acre
 * Claerwen Reservoir — 655 acre
 * Clywedog Reservoir — 601 acre
 * Nant-y-moch Reservoir — 525 acre
 * Caban Coch Reservoir — 519 acre

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

By counties and county boroughs
This list of Welsh lakes ordered by principal areas (counties and county boroughs) includes lakes with a surface area of greater than 5 acre, 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 principal area 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 (*).

Powys
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.

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

By supply to England
Many Welsh lakes supply the nation itself with water, however, some lakes and reservoirs supply England.

The main reservoirs created for this purpose include: