There are fifteen of them, each made from roundwood timber no wider than ten centimetres, driven into the clay at intervals ranging from half a metre to nearly two metres apart. Taken individually, they look like almost nothing. Understood as a group, they are the skeletal remains of a fish weir, one of the quieter and more easily overlooked forms of early industry that once worked the tidal rivers of Ireland.

A stake-net weir of this kind operated by exploiting the rhythm of the tide. Posts were set into the riverbed or its margins in a line or gentle curve, and nets were fixed between them. As the tide ebbed, fish moving with the current were guided into or against the net and caught. The technique is ancient in principle, though the Mellon weir itself is thought to date from the nineteenth century, according to the archaeologist Aidan O'Sullivan, who described it in a 2001 survey. The posts are oriented roughly northeast to southwest, and the weir sits in estuarine clays on the western bank of the Maigue, approximately sixty metres northwest of a second, similar structure. The proximity of the two weirs to one another suggests a stretch of river that was actively and systematically worked, rather than a single opportunistic installation.

The Maigue flows through low, quiet farmland before reaching the Shannon estuary, and this stretch near Mellon is not a place that announces itself. The weir is only really visible when the tide is out, and the posts, being made of timber rather than stone, are unobtrusive even then. Anyone approaching should expect soft ground and an estuary landscape more defined by mud and reed than by drama. The site is of interest less as a spectacle than as a physical record of how people once extracted a living from a tidal river, using materials close at hand and methods calibrated precisely to the water's movement.