Llyn Cwellyn - Betws Garmon

Llyn Cwellyn (Llyn Quellyn in some antiquated texts) is a reservoir in North Wales which supplies drinking water to parts of Gwynedd and Anglesey. It lies on the Afon Gwyrfai in Nant y Betws between the Snowdon Massif and Mynydd Mawr in the northern part of Snowdonia National Park. It has an area of 215 acres (0.87 km2), and is over 120 ft (37 m) deep. At the southern end is the small village of Rhyd Ddu.

Although it is now dammed at the northern end, below the Castell Cidwm ridge, near the village of Betws Garmon this has not substantially increased the size of the natural glacial moraine lake that has existed since the last ice age. The lake also is home to brown trout and there are otters that are regularly seen at the Castell Cidwm end. The lake has shared ownership between Lawrence Jones owner of the Castell Cidwm estate at the Northern end and Welsh water, who own the right hand side that supplies the weir. The lake was originally owned by the Marquis of Anglesey who used the Castell Cidwm country house as his hunting lodge.

The A4085 runs past the lake, however there are no lay-byes for picnics and the east side is now considered a Nature Reserve and fishing is not