It measures roughly 21 metres east to west and 16 metres north to south, rising only about one and a half metres above the lake surface, and its surface shows no obvious signs of having been shaped by human hands. Yet it appears on the 1907 edition of the Ordnance Survey six-inch map labelled as both a crannog site and as 'Crane Island', a name that quietly preserves a memory of deliberate, ancient occupation that the vegetation and earthwork have since swallowed.

A crannog is an artificial or artificially enlarged island, typically built during the early medieval period in Ireland as a defended homestead or place of refuge, constructed from layers of timber, stone, peat, and brushwood anchored in shallow or deep water. That this particular example leaves no visible trace of such construction is not unusual; centuries of vegetation growth, waterlogging, and sediment accumulation frequently obscure the original fabric entirely. The sole physical object recovered from the island to date is a fragment of a grindstone, found during an investigation in 1969 and noted by A. T. Lucas in 1972. A grindstone, used for sharpening tools or grinding grain, is a modest but telling find, the kind of everyday domestic object that suggests sustained habitation rather than occasional use. A second possible crannog lies approximately 40 metres to the north-west of the island, and the two together point to this stretch of St John's Lough as a place that once held real strategic or domestic significance for the people who chose to build in its waters.