- Category: Water Feature
- Type: Inland Water
- Latitude/Longitude: 52°46'57"N 3°30'37"W
- Eastings/Northings: 298227, 321643
- OS Grid: SH982216
- Mapcode Local: GBR 6H.XRS0
- Mapcode Global: WH67T.1BN1
Location and coordinates are for the approximate centre of Llyn Efyrnwy within this administrative area.
Geographic features and populated places may cross administrative borders.