Tal-y-Llyn is a glacial lake in Snowdonia, mountain range of Gwynedd, Wales. It has a surface of 89 ha (220 acres) and its average depth is 3 m (9.8 feet). The lake is known for its brown trout. It has been the home to a family of otters, too. Nearby Talyllyn Railway can be found, which has its eastern terminus near the village of Abergynolwyn, in the range of the parish of Tal-y-llyn. River Dysynni runs from the lake, through Abergynolwyn, and drains into the sea near Tywyn.