Lough Erne, the great chain of island-strewn lakes spreading through County Fermanagh, takes its name in Irish legend from a woman called Erne — a lady-in-waiting, the tradition says, to the warrior-queen Medb at her royal seat of Cruachan in Connacht. The story of how the lake came to be is one of the etiological myths so common in Ireland, in which a feature of the land is explained as the drowned, dissolved body of a goddess or noblewoman.
The story
The tale tells that Erne and a company of her maidens were at Cruachan when terror came upon them: a fearful monster — in the tradition, a being that emerged from the cave of Oweynagat (the 'Cave of the Cats'), the famous Otherworld entrance at Cruachan that breathed out destructive creatures at Samhain. Fleeing the horror in panic, Erne and her maidens ran northward, away from Connacht, until they came to a river, where they were overwhelmed and drowned. Their bodies, the legend says, dissolved into the water and spread out across the low country, and from them formed the broad waters of Lough Erne, which has carried her name ever since.
Scholars connect the name more deeply still to an ancient goddess Érann, eponymous deity of the Érainn, one of the early peoples of Ireland, so that Loch Éirne may mean 'the lake of the goddess Érann' — the drowning-legend a folk-memory of a divine figure whose power dissolved into the water to give life to the land. Either way, the great lake of Fermanagh keeps in its very name the memory of a woman of myth who fled a monster and became the water itself.