It is not a wall or a stone trap but a post-and-wattle fence, the kind of structure built by driving upright posts into the riverbed and weaving flexible branches between them to create a barrier that would funnel fish into a confined area as the tide dropped. Four metres long and oriented roughly east-northeast to west-southwest, it sits on the western bank of the channel, roughly equidistant between a small creek to the north and Little Quay Island to the south.

The weir was recorded by Aidan O'Sullivan in February 1997 and published in 2001 as part of his survey of intertidal archaeology along the Irish coastline. He dated it broadly as medieval or post-medieval, a range that reflects the difficulty of pinning down such structures without excavation or dendrochronological sampling. Fish weirs of this general type were used widely around Ireland's estuaries and tidal rivers throughout the medieval period and well beyond, exploiting the natural rhythm of the tides rather than requiring boats or nets. The location here, on tidal clays at the low-water mark, is exactly where such a structure would have been placed, positioned to intercept fish moving with the flood tide and strand them as the water receded. That the wattle elements survived at all is a small matter of note; organic materials in intertidal zones are preserved by waterlogging and anaerobic conditions in the mud, but they remain vulnerable to erosion and disturbance.