It looks, at a glance, like a natural feature, a clump of vegetation rising from the water. It is not. The island is a crannog, an artificial or partially artificial lake dwelling, built up from timber, peat, brushwood, and stone, and used at various points throughout Irish prehistory and the early medieval period as a place of habitation, refuge, or high-status settlement. The fact that it blends so readily into its surroundings is part of what makes it easy to overlook.

Crannogs were constructed across Ireland and Scotland for thousands of years, with many examples in Cavan sitting in the lakelands that define the county's landscape. They were typically reached by boat or by a submerged causeway, making them naturally defensible. The one in Disert Lough is modest in scale, just twelve metres in diameter, but its circular form is characteristic of the type. Today it is heavily overgrown, its archaeological character obscured beneath dense vegetation, which is a common fate for crannogs left undisturbed. That overgrowth is, in its own way, a form of preservation, keeping the underlying structure largely intact beneath the surface.