Pollatoomary is the deepest explored underwater cave in Ireland. First discovered in 1978 by cave diver Martyn Farr, it was explored to a depth of 103 metres (338 ft) by Artur Kozłowski, one of Farr's students, on 5–6 July 2008.
The cave is located in the Partry Mountains in the townland of Bellaburke near Killavally, Westport, County Mayo, where the Aille River reemerges, having gone underground at Aille caves some 4 kilometres (2.5 mi) away. The cave entrance is on privately owned farmland.
The explored limit of Pollatoomary is 13 metres (43 ft) deeper underwater than that of the terminal sump in Wookey Hole Caves in Somerset, England, which had previously held the record for the deepest underwater cave in Britain and Ireland.