The Battle of Bloody Bay, or Blàr Bàgh na Fala in Scottish Gaelic, was a naval battle fought near Tobermory, Scotland. It was fought on the coast of Mull 2 miles north of Tobermory, between John MacDonald of Islay, the Lord of the Isles and chief of Clan Donald; and his son, Angus Og Macdonald. The precise date of the battle varies in sources, from 1480 to 1483. After the battle, in which Angus Og Macdonald emerged victorious, the latter seized power from his father, and held it for the rest of the decade. However, Angus's victory would prove pyrrhic. Many clansmen had died in the battle and nearly half the clan's fleet had been sunk, as a result of which the power of the Lords of the Isles was henceforth greatly diminished. Angus, last of the independent Lords of the Isles, would himself be murdered in 1490.

John of Islay (1434–1503), Earl of Ross, fourth Lord of the Isles, and Mac Domhnaill, was a pivotal figure in late medieval Scotland: specifically in the struggle for power with James Stewart, James III of Scotland, in the remoter formerly Norse-dominated regions of the kingdom. His defeat in this conflict led to rebellion against John by his illegitimate son Angus Óg, resulting in the defeat of John's fleet at the Battle of Bloody Bay in the early 1480s. Thereafter and until his death in 1503 John remained an inconsequential figure while, until his murder in 1490, Angus continued to dominate the affairs of Clan Donald. In 1493 James IV brought the Lordship of the Isles to an end.