It is a fish weir, a type of trap built to exploit the rhythm of the tides: as water retreats, fish are left stranded within the enclosure, making them easy to collect by hand or net. What makes this one quietly arresting is the precision of its design, laid directly onto sloping natural bedrock and shaped to do specific work at specific points along its perimeter.

The construction follows a subrectangular plan, but several deliberate features complicate that basic outline. At the eastern end, which is where the trapping action happens, the wall bends back south-westward, funnelling fish inward rather than letting them escape as the tide drops. Midway along the seaward side, a semicircular bulge roughly 17 metres across projects outward, with a gap at its centre, likely a sluice or entry point that allowed fish in while controlling the flow. At the north-east corner, the wall flares outward again in a V shape, a further refinement in what is clearly a considered piece of coastal engineering. The structure is classed as post-medieval, and there is reason to believe it was still being actively used within the last fifty years, which places it in an unusual position: ancient in principle, but recent enough that someone living today may well remember pulling fish from it.

The weir sits about 2.3 kilometres south-west of Carrigaholt, and because it is built on tidal bedrock it will only be fully legible at low water, when the walls emerge from the bay and the geometry of the whole structure becomes visible. The V-shaped extension at the north-east corner and the semicircular gap along the seaward face are the details worth looking for; together they give a clear sense of how the trap was intended to function, guiding fish through the gap and into the enclosed area from which there was no easy retreat.