In the mythology of early Ireland, the formation of Lough Neagh — the largest lake in the British Isles, spreading across five Northern Irish counties — was bound up with the legend of Lí Ban. She was the daughter of Eochaidh mac Mairidh, a king of Ulster whose palace stood where the lake now lies. A sacred well on the estate had been left uncovered one night, and the water burst free in a great flood that killed Eochaidh and all his household. Lí Ban survived for a year in an air-locked chamber beneath the waves, listening to the world of fish and current, until she prayed to be transformed into their kind. The prayer was answered: from that day she swam as a salmon from the waist down, her upper body and face remaining human. Her lap-dog, companion through the years of isolation, was similarly transformed into an otter.
The story
For three centuries Lí Ban roamed the seas between Ireland and Scotland, her singing said to be of unearthly beauty. In the time of St Comgall of Bangor (6th century), a monk named Beoan heard her angelic voice while out on the water near what is now Larne on the Antrim coast and reported it to the abbot. A party was sent to find her; Lí Ban agreed to come ashore at a place called Ollarba, was baptised Muirgen — meaning 'sea-born' — by a bishop, and died almost immediately, ascending to heaven as a saint. She had chosen the brevity of a Christian soul over another three hundred years of immortal swimming.
The legend is recorded in multiple early Irish annals and hagiographic sources, and the Dúchas Schools' Collection preserves oral variants gathered from County Antrim and Derry communities in the twentieth century. Lí Ban is venerated as a saint on 27 January in the Martyrology of Tallaght, one of the earliest Irish saints' calendars. Her legend is notable for bridging pagan and Christian tradition in a single narrative arc: she is simultaneously a water spirit whose origins lie in the pre-Christian sacred well cult, and a baptised saint who earns her place in heaven. Lough Neagh takes its Irish name Loch nEachach from her drowned father Eochaidh. The Seamus Heaney HomePlace in County Derry has featured the legend as part of its survey of Ulster's mythological heritage.