Llyn Conwy lies at a height of about 1,488 ft, with a maximum depth of 16 feet, and is by far the biggest lake of the Migneint moors, an extensive area of blanket mire with high rainfall - about 260 cm p.a.

This is an area of Ordovician rocks, lending its name to the "Llyn Conwy Formation", which is identified by its yellowish rhyolitic tuffs.

[2][3] This Formation also reappears in Afon Tryweryn to the south-east, where the hard rock was utilized in the construction of Llyn Celyn dam.

[4] Llyn Conwy is owned by the National Trust and, whilst a natural lake, is managed as a reservoir by Welsh Water.

[11][12] Whilst the lake is often regarded in a general sense as the source of the river Conwy, much of this area of the Migneint blanket bog contributes water to its uppermost reaches.

[1] The largest two of these, which enter the lake on its north-western and eastern shores, can be followed for over ¼ mile to the upper edges of the basin, even during drier periods.

A small parapet with a sluice-gate, hardly worthy of the word "dam", controls the outflow from the southern end of the lake, the level of which has not changed since the early 19th century Ordnance Survey.

A right turn from Ffestiniog leads to an old house called 'Llyn Cottage' (often used for night fishing by Lord Penrhyn and his friends), where there is parking and an access path to the lake.