Satellite imagery, including orthophotos captured between 2010 and 2013, reveals the form with a clarity that ground-level inspection rarely affords: a roughly D-shaped enclosure measuring approximately 37 metres east to west and 31 metres north to south, defined by an earth and stone bank that curves around the southern promontory of the island. It is the kind of feature that blends into farmland almost entirely until geometry gives it away.

The monument belongs to a broader tradition of promontory and cliff-edge forts found along Irish coastlines and riverbanks, where defenders used natural topography to reduce the amount of artificial barrier they needed to construct. A straight or curved bank across the accessible landward side, combined with the natural drop of a promontory, created a defensible enclosure with relatively modest effort. On Greenish Island, the bank closes off the southern tip, and a much larger enclosure sits some 85 metres to the north, recorded separately in the Sites and Monuments Record. The relationship between the two features is not fully documented, though their proximity on a strategically positioned island at a major river confluence is unlikely to be coincidental. The site was compiled by Caimin O'Brien and uploaded to the national record in July 2020, suggesting it received formal attention relatively recently.

Greenish Island lies in the Shannon Estuary in County Limerick, in an area of tidal flats and low-lying farmland. Access to the island is not straightforward, and visitors should research current conditions before attempting to reach it, as tidal and land-access factors vary. The earthwork itself sits in pasture on the southern end of the island, so appropriate footwear is advisable. The D-shape is subtle at ground level, but the line of the bank becomes legible once you know what you are looking for, particularly where vegetation follows the curve of the old earthwork.