Measuring roughly 16 metres north to south and 11 metres east to west, it rises about 0.6 metres above the waterline, dry underfoot, and carpeted in meadowsweet. Its geometry and composition suggest it was put there deliberately by human hands, making it a probable crannog, one of the artificial or semi-artificial islands that were constructed in Irish and Scottish lakes from the Bronze Age through to the early medieval period and sometimes beyond, serving variously as defended homesteads, storage platforms, or high-status residences.

Crannogs were typically built by piling timber, brush, stone, peat, and other materials into shallow water, sometimes anchored with wooden stakes, and they are found in considerable numbers across Ireland. The Ballindooly example has not been excavated or definitively confirmed, and so its date and original purpose remain open questions. It is worth noting that the lake does contain one other island, a larger, tree-covered feature on the south-western fringes, but that one is entirely natural in origin, which makes the contrast with the smaller, flatter platform near the southern shore all the more telling. The regularity of the oblong outline is what draws the eye and prompts the question.