It is a V-shaped structure, around thirty metres long, built from posts driven into the foreshore and woven through with wattle, a technique that would have been familiar to anyone working these waters in the post-medieval period. The logic of the design is simple and effective: the open end of the V faces the incoming tide, fish are funnelled inward as the water rises, and as the tide retreats they are left stranded in the narrowing apex, where they can be collected by hand or net.

Recorded in July 2000 and described by archaeologist Aidan O'Sullivan, the weir is oriented roughly north-northeast to south-southwest and sits on the upper foreshore to the northwest of Bush Island. Fish weirs of this kind were once common along Irish estuaries and tidal inlets, representing a form of communal or local food production that left few written records but considerable physical traces. The post-and-wattle construction, perishable by nature, makes survival of any kind relatively rare, and the Shannon estuary has proved a particularly productive environment for preserving such features in waterlogged and anaerobic foreshore conditions.