A fish weir is essentially a fixed trap, typically constructed from timber stakes, woven withies, or stone, arranged to funnel fish into an enclosed space where they can be retrieved with ease. The remains of such structures along the Shannon represent some of the oldest infrastructure in Ireland, predating roads, bridges, and much of what we think of as organised settlement. To find one recorded as a monument on the Clare bank of the river is to catch a glimpse of an economy measured not in currency but in catch.

Fish weirs on the Shannon have a long documented history, with medieval annals and ecclesiastical records frequently referencing the fishing rights attached to particular stretches of the river. Monasteries were often the primary beneficiaries, holding weir rights as a significant source of income and sustenance. Salmon and eel were the principal target species, eels especially being a commodity of considerable value in pre-modern Ireland, traded, taxed, and rendered as rent. The physical remains of weirs can persist for centuries, as stone and timber driven into riverbed sediment are sometimes preserved in conditions that would destroy almost anything else.