Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Tal-y-llyn Lake, also known as Talyllyn Lake or Llyn Mwyngil, is a large glacial ribbon lake formed by a post-glacial massive landslip damming up the lake within the glaciated valley. It is situated at the foot of Cadair Idris, in the Snowdonia mountain range of Gwynedd, Wales. The River Dysynni flows from the lake, through the village of Abergynolwyn, and discharges into the sea north of Tywyn.