They are the remnants of a post-medieval jetty, modest in scale but quietly suggestive of a working waterfront that has long since disappeared. The exposed length runs to roughly 26 metres, with the posts, each between 15 and 25 centimetres in diameter, spaced at intervals of about 1.5 to 2 metres. Below low water, the structure may curve around to the east, meaning that what is visible at any given moment is only part of the whole.

The jetty was recorded by Aidan O'Sullivan in February 1997 and documented in his 2001 study of the region's intertidal archaeology. The Shannon estuary has a long history of small-scale maritime activity, and structures of this kind, driven timber piles set into tidal mud to form a landing place, were once a practical necessity for island communities and estuarine settlements that depended on boat traffic for trade, transport, and fishing. The post-medieval period broadly covers the sixteenth to eighteenth centuries, though pinning a more precise date to a timber jetty without dendrochronology or other analysis is difficult. What the posts do confirm is that Quay Island, whose very name implies a history of loading and unloading, once had infrastructure to match that function.