Boa, or Badhbha, Island is the largest of the islands of Lower Lough Erne and is situated to the north of the Lough close by the modern border with the Republic of Ireland. Until the late 1920s the island was not connected to the mainland and the only way to travel was by boat, with farmers swimming their cattle and horses to markets and grazing on the mainland. Today, the main A47 Boa Island Road connects the island to Kesh and Enniskillen in the east and Belleek in the west of Fermanagh. The road was built out of political expediency, connecting Enniskillen, the county town of Fermanagh with the north-west part of the county, without having to traverse Irish Free State territory. It also meant that troops could be moved by road instead of an amphibious landing which had taken place at the Battle of Pettigo in 1922.
Boa Island before the A47 bridges were built
I have traced the O’Donnell family back to around 1850 on Boa Island - it could go back generations further, but there are so many brick walls when you are searching for records in Ireland. They either don’t exist, were never recorded in the first instance, lie in private collections or are split between the authorities in Northern Ireland and the Republic. The farmstead stands on a promontory called Gubbakip (more of which I will write at a later date) and is still in the hands of the family in the shape of Desmond O’Donnell my 1st cousin 1x removed and his wife Breege.
The passage below is from volume 3 of an edition of The Annals of the Kingdom of Ireland by The Four Masters (from the earliest period to 1616) edited by John O’Donovan. This edition was publsihed in 1853 and is out of copyright and available for free on Google Books. The Annals were compiled between 1632 and 1636 in the Franciscan Priory in Donegal Town by Mícheál Ó Cléirigh (a Franciscan friar), Cú Choigcríche Ó Cléirigh, Fearfeasa Ó Maol Chonaire and Peregrine Ó Duibhgeannain. The work was commisioned by Fearghal Ó Gadhra, a lord in Co. Sligo and they are important in giving the Gealic view on important events in Irish History. The O’Donnell activity described in the small passage would be nothing unusual; they were styled Princes of the neigbouring territory, Donegal and would have had extensive rights and claims stretching into Fermanagh, Sligo and Tyrone amongst others. The translation and notes are O’Donovan’s.

THE AGE OF CHRIST 1369
O’Muldoon (Donnell), Lord of the territory of Lurg, was slain by the sons of Niall O’Donnell, who carried the spoils of his territory with them to one of the islands of Lough Erne which is called Badhba (1). Phillip Maguire, Lord of the Seven Tuathas (2), set out with a large fleet to take revenge upon the sons of O’Donnell for the death of his Oglach (3); and a naval engagement took place, in which Niall Oge, son of Niall Garv, the son of Hugh, son of O’Donnell Oge [O’Donnell], was slain on Finn-loch (4), close to the island.
(1) Badhbha. - This island still retains this name, but it is generally anglicised Boa Island. It is usually called by the natives of Tuath Ratha dwelling on the south side of Lough Erne, opposite this island, who speak Irish well. It is the largest island in Lower Loch Erne, and is situated not far from its northern shore, a short distance to the south of the village of Pettigoe.
(2) The Seven Tuathas, i.e. the seven Tuathas, or districts, comprised in the principality of Fermanagh, of which Maguire was, at this period, the chief lord.
(3) Oglach. - This word literally means, a young hero or soldier; but it is often used in the sense of vassal, such as O’Muldoon was to Maguire. From Oglac, in this sense, is derived oglacar, vassalage, servitude.
(4) Finn-Loch. - i.e. the white lake. This was evidently the name of Lower Lough Erne, which might have been locally so called to distinguish it from Upper Lough Erne, as being a brighter sheet of water, and less studded with islands.
Annals of the Kingdom of Ireland (Google Books)