The uncertainty is itself the story.

A crannog is a man-made island dwelling, typically constructed from timber, brushwood, and stone, and used throughout Ireland from the Bronze Age well into the early medieval period as a defensible home or place of refuge. When the Ordnance Survey produced its six-inch map in 1834, the lake at Carrickmore was recorded as a small but distinct pot lake, roughly one hundred metres across, with a circular island sitting at its centre, approximately ten metres in diameter. Even then, the lake was probably a shadow of its original self; estimates suggest it once extended to around two hundred metres across. Since that survey, the water has contracted further still, to a narrow oval measuring roughly fifty metres at its longest and twenty-five metres wide. The island, if it persists beneath the surface, leaves no visible trace. The shrunken lake is noted as dangerous, and no indication of any antiquity is now apparent above the waterline.