Llynnau Mymbyr are two lakes located in Dyffryn Mymbyr, a valley running from the village of Capel Curig to the Pen-y-Gwryd hotel in Snowdonia, North Wales. The A4086 runs along their northern banks.
Strictly speaking this is one lake, originally called Llyn Mymbyr, with a maximum depth of 30 feet. About 3/4 mile long in total, a delta has built up midway along the north shore, and this has to all purposes cut the lake in two - hence the plural name.
The river feeding the lakes is the Nantygwryd (or Nant-y-gwryd), which has its source at Llyn Cwm-y-ffynnon, also marked on maps as the Nant Gwryd, which is a tributary of the Afon Llugwy. The two rivers join at Capel Curig.
The lake was used for fly-fishing and sub-aqua courses in the 1960s and is still used today as a canoe training resource by Plas y Brenin and other Local Education Authorities.