It is not a dramatic structure by any measure, but its very smallness is part of what makes it interesting. This is, in all likelihood, the remnant of a creek trap, a form of fish weir designed not to span an open river but to intercept fish moving through a tidal inlet or narrow channel at the margins of an estuary.

Fish weirs of this type work on a straightforward principle. Posts are set into the riverbed or tidal flat and woven with wattle or strung with netting to form a barrier, guiding fish, typically eel, salmon, or flatfish, into an enclosure from which they cannot easily escape as the tide recedes. The technique is extremely old, used widely around the Irish coast and along major river systems from the early medieval period onwards, though many examples are difficult to date without excavation. The Mellon weir was recorded and described by Aidan O'Sullivan in 2001, who catalogued it as a post alignment consistent with a small creek trap, though the precise age of the structure does not appear to have been established from the published notes alone.

Access to this kind of intertidal feature depends almost entirely on the tide, and that is worth bearing in mind before making the trip. Estuarine clays expose and conceal features like this on their own schedule, and what is visible at low water on one visit may be submerged or silted over on another. The site lies south of Maiden Rock, which provides the main navigational reference point. Anyone with an interest in early fish traps or intertidal archaeology along the Shannon would find this worth seeking out, though patience with tidal timing and a willingness to pick across estuary mud are more or less mandatory.