Llyn Melynllyn (Welsh for yellow lake) is a lake within the Carneddau range of mountains in Snowdonia, North Wales. It lies at a height of just over 2,000 feet (610 m), and has an area of some 18.5 acres (75,000 m2). Cliffs rise steeply from its western edge, up to the summit of Foel Grach, and down from which most of its feeder streams flow. A small dam was built at its northern end in 1887, but this was deliberately breached in 1970. The lake acts as a reservoir for the Llandudno area. Less than a kilometre to its north lies the larger Llyn Dulyn.