It is not a jetty or a boundary marker. It is the skeletal remains of a fish weir, a structure once used to trap fish on a falling tide, and it has sat largely unnoticed in the intertidal zone beside the townland of Portdrine in County Clare for centuries.

A post alignment of this kind works by guiding fish into a confined area as the tide retreats, leaving them stranded and easily harvested. The Portdrine weir runs on a northwest to southeast orientation, a alignment likely chosen to work with the particular tidal flow along this stretch of the estuary. Recorded in March 1999 and documented by Aidan O'Sullivan, the structure was identified as post-medieval in date, though the possibility of a medieval origin has not been ruled out. That ambiguity is itself telling: fish weirs were a fixture of Irish coastal and estuarine life from early medieval times onward, and their basic form changed little across the centuries, making precise dating without excavation genuinely difficult. The posts survive in the estuarine clay, a low-oxygen, waterlogged environment that can preserve organic material far longer than dry land would allow.