It is the skeleton of a fish weir, a post-medieval structure designed to trap fish as the tide retreated, and it has survived long enough in the estuary sediment to still be measurable and mappable.

Fish weirs of this kind work by using a fixed barrier, typically a line of stakes interwoven with wattle or netting, to guide fish into a confined area or trap as water levels fall. What makes this particular example technically interesting is the deliberate engineering visible even in its ruined state. The posts are set with oblique braces on both sides, but the downstream side uses noticeably heavier timbers, a detail that reflects the practical reality of tidal force: the downstream face bore the greater hydraulic load as water drained seaward. Aidan O'Sullivan, who documented the structure in July 2000, recorded these specifics and placed it within the broader post-medieval tradition of intertidal fish trapping on Irish estuaries, a practice that was once widespread along the Shannon but of which few physical traces now remain.