Loch Nafooey (Irish: Loch na Fuaiche, meaning “Lake of the winnowing winds” or “grave-shaped lake”) is a rectangular shaped glacial lake in County Galway. Part of the north-eastern shore lies along the border to County Mayo. The closest village is Finny (Irish: Fionnaithe, meaning “places of rank vegetation”), County Mayo with the Galway village of Leenaun about 11 km away.

Approximately 4 km long and 0.8 km wide, Loch Na Fooey is set in a steep-sided valley, surrounded by the mountains of Galway to the south and Mayo’s Partry Mountains (Sliabh Phartraí in Irish) to the north. A number of rivers feed the lake, including the River Fooey (in Irish Abhainn na Fuaiche), which rises from the Devil’s Mother mountain and enters the lake at the western shore. The Finny River, rising from the south-east of the lake drains into the southwest of part Lough Mask. Many mountain streams flow into the lake. The lake has a small sandy shore on its western end.

The area around Loch Na Fooey is known as the site of the ancient “Finny volcano” (490 million years ago), formed as the Iapetus Ocean closed to bring the two halves of Ireland together. The volcano’s landform is now gone but some of the volcanic rocks are preserved in the area, including pillow lavas, and breccia.
There is a small funnel-shaped island close to the south-eastern shore known as Red Island (An tOileán Rua). The waters hold a range of fish including wild brown trout and pike.
The locality has a number of walks, both for experienced hill walkers and others.