The structure is modest in scale, a possible alignment of posts with interwoven rods, roughly eight metres long, crossing a small tidal creek in an east-west orientation. It is the kind of thing that rewards a patient eye rather than a casual glance.

A fish weir of this type works by passive entrapment: stakes are driven into the riverbed or estuary floor and woven through with flexible rods, forming a barrier that channels fish into a confined space as the tide recedes. The technique is ancient, and examples have been recorded at many points along the Shannon, but the Graigue Island structure is considered possibly post-medieval in date, suggesting it may have been in use sometime after the sixteenth century. It was documented in July 1994 by Aidan O'Sullivan, whose 2001 survey of intertidal and wetland archaeology along the Shannon recorded the weir's location approximately one hundred metres to the north-east of Graigue Island itself.