It is the kind of structure that registers only as a pattern of dark timber at the waterline, easy to miss unless you know what you are looking for.

A fish weir of this type works through geometry. Two fences of timber stakes and wattle form a wide angled enclosure, directing fish inward as the tide falls and preventing their escape as the water drops. Here, the flood fence runs roughly northwest to southeast at around ten metres in length, while the shore fence extends north to south for approximately 120 metres, the two meeting at an angle of about sixty degrees. Recorded in July 2000 and described by archaeologist Aidan O'Sullivan, who surveyed intertidal archaeology along the Shannon in his 2001 study, the weir dates to the post-medieval period, meaning roughly the sixteenth century onward. The estuarine clays that hold the surviving timbers are themselves part of why such structures endure; waterlogged, anaerobic mud is a remarkable preservative, and the Shannon's tidal margins have yielded a number of similarly ancient wooden fish traps along their length.