Llyn Mair (Welsh  for 'Mary's lake') is a  artificial lake near Maentwrog, in Gwynedd in North Wales (grid reference ). It lies in the area of Tan-y-Bwlch, a little above Plas Tan-y-Bwlch, and is in the catchment area of the River Dwyryd.
Llyn Mair, meaning "Mary's lake" in Welsh, is an artificial lake located near Maentwrog in Gwynedd, North Wales. It sits within the Tan-y-Bwlch region, slightly above Plas Tan-y-Bwlch, and falls under the River Dwyryd's drainage basin.