Aasleagh, Waterfall on River Erriff in County Mayo, Ireland.

Aasleagh is a waterfall on the River Erriff in County Mayo where water cascades over multiple rocky steps, creating white water patterns against dark stones. The river continues its journey toward Killary Harbour beyond the falls, forming a dramatic natural feature in the valley.

The name Eas Liath, meaning "grey waterfall", is Irish in origin. The falls and the nearby village of Leenaun served as filming locations for the 1990 film The Field, starring Richard Harris. In Irish mythology, the horses of Cú Chulainn, Liath Macha and Dub Sainglenn, were said to have emerged from the Linn Liaith, a grey pool that some, though controversially, link to Eas Liath.

The name Eas Liath means "grey waterfall", from Irish eas (waterfall) and liath (grey). In the Ulster Cycle, the horses of Cú Chulainn, Liath Macha and Dub Sainglenn, were said to have emerged from the Linn Liaith, the "grey pool", and returned there after his death; one disputed identification links that pool to these falls.

The falls sit just off the N59 road northeast of Leenaun, at the boundary between County Galway and County Mayo, where the Erriff meets the head of the Killary Fjord. Aasleagh Lodge, the 18th-century house beside the falls, is run as a fishing lodge by the regional fisheries board, and the Erriff is known for its salmon.

The falls form part of the Western Way hiking route, a long-distance trail that passes through the Erriff Valley. Many hikers use this location as a stopping point while traversing one of the region's most scenic valleys.