A crannog is an artificial or partially artificial island, typically built from timber, stone, peat, and brushwood during the early medieval period, and used as a defensible dwelling or place of refuge. The example recorded here was never large to begin with, roughly five metres across, and sat barely five metres from the north-eastern shore of the lough.

The sole evidence for its existence comes from the 1837 edition of the Ordnance Survey six-inch map, where it appears as a small circular island, carefully noted and presumably observed by the surveyors at the time. Whether it had already lost its identity as a constructed feature by then, or whether local knowledge of its origins had simply faded, is unclear. What is certain is that it is not visible now, and those living near Derrynasallagh Lough, a long narrow body of water running roughly five hundred metres north to south and about two hundred and fifty metres east to west, do not associate the spot with any crannog at all. The most likely explanation is that the structure has gradually merged with the lakeshore over the intervening centuries, its materials slumping and spreading until the boundary between island and bank became indistinguishable.