is a lake in the Carneddau range of mountains in Snowdonia, North Wales.
It lies at a height of about and covers an area of some . It has a maximum depth of .The Lakes of Eryri, by Geraint Roberts, Gwasg Carreg Gwalch, 1985
Since the early twentieth century water has been taken from its outflow, the River Llugwy to feed Llyn Cowlyd via a series of leats.
Since the mid-1970s the lake has additionally acted as a reservoir for Bangor and eastern Anglesey, which necessitated the laying of a pipeline some long to the water treatment works at Mynydd Llandygai.Cyfrinachau Llynnoedd Eryri, by Geraint Thomas, y Lolfa, 2011
It is the source of the River Llugwy which flows via Capel Curig and Betws-y-Coed before becoming a tributary of the River Conwy.
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