Fish weirs are among the oldest and most practical of human constructions: barriers of stone, timber, or wattle built across tidal channels or rivers to trap fish as the water recedes, requiring no nets and no boats, only patience and a working knowledge of the tide. They were in use in Ireland from at least the early medieval period, and examples have been found preserved in coastal mud and riverbanks across the country, often invisible except at low water or in drought conditions.

Derryeighter sits in County Galway, a county whose western edge is deeply cut by inlets, loughs, and river systems that would have made fish weir construction both practical and necessary for communities dependent on freshwater and coastal resources. The weir at Derryeighter is a recorded monument, meaning it has been identified and listed as part of Ireland's archaeological heritage, though detailed documentation on this particular structure remains sparse at present.