The lake contains two islets, of which one was a crannog and the other the site of an ancient kirk.
In the crannog of Lisnacroghera, county Antrim, iron swords, with sheaths of thin bronze ornamented with scrolls characteristic of the Late Celtic style, iron daggers, an iron spear-head 162 in.
Among the few remains of lacustrine settlements in England and Wales, some are suggestive of the typical crannog structure.
Under the year 848 the Annals of the Four Masters record the burning of the island of Lough Gabhor (the crannog of Lagore), and the same stronghold is noticed as again destroyed by the Danes in 933.
The crannog of Lochlee, near Tarbolton, Ayrshire, explored by Dr R.
A crannog in Loch-an-Dhugael, Balinakill, Argyllshire, described by the same explorer in 1893, revealed a substructure similar to that at Lochlee, with a double row of piles enclosing an area 45 to 50 ft.
The crannog of Lagore, the first discovered in Ireland, was examined and described by Sir William Wilde in 1840.
In the crannog of Lagore, county Meath, there were about 150 cartloads of bones, chiefly of oxen, deer, sheep and swine, the refuse of the food of the occupants.
Under the year 1246 it is recorded that Turlough O'Connor made his escape from the crannog of Lough Leisi, and drowned his keepers.
The crannog of Cloonfinlough in Connaught had a triple stockade of oak piles, connected by horizontal stretchers and enclosing an area 130 ft., in diameter, laid with trunks of oak trees.