Measuring roughly sixteen metres north to south and eighteen metres east to west, it appears to have been deliberately built up from stone rather than deposited by any geological process. In winter, rising lake levels submerge it almost entirely, so what reads on a summer visit as a low, brooding presence in the water effectively disappears with the season.

Crannogs, artificially constructed lake islands typically built from timber, stone, brush, and peat, were used in Ireland from the Bronze Age through to the early modern period, serving variously as defended homesteads, places of refuge, and high-status residences. This example in Lough Mask retains visible traces of its structure: four timber posts remain upright in the north-eastern part of the site, and nine cross beams, orientated east to west, protrude through the accumulated earth and stone on the southern side. A breakwater extends to the south-west, suggesting the builders were managing the island's exposure to the lake's prevailing conditions. The details were recorded in D. Lavelle's 1994 archaeological survey of the Ballinrobe district, which catalogued sites around Lough Mask and Lough Carra.

The site is most accessible and most legible in the drier months, when lake levels drop enough to expose the stonework and the protruding timbers. Even then it sits only a short distance offshore, easy to spot from the eastern shore of Cushlough Bay but not easily reached without a boat.