A weir built to catch them has been here in some form since at least the early sixteenth century, and the infrastructure it belonged to, dams, mills, waterways shaped to serve commerce, has left its mark on the physical character of the river at this point even now.

The earliest record of the weir comes from 1524, when a salmon weir at Chapelizod was granted to Sir William Wyse of Waterford, according to the historian Arthur Went, writing in 1954. Wyse was a Waterford merchant of considerable standing, and the grant of a salmon weir this far up the Liffey speaks to how valuable a controlled stretch of river could be. The site appears again in the Civil Survey of 1654 to 1656, a Cromwellian-era land inventory that catalogued property across Ireland, which records a salmon weir on the Liffey at Chapelizod. Researchers have suggested this weir was probably connected to the mill dam that served the local milling industry, a practical arrangement in which the same structure that impounded water for grinding grain also intercepted fish moving upstream. A fish weir is essentially a fixed trap, often built from stone or timber, designed to funnel fish into a confined channel or basket where they could be harvested; combining one with a mill dam made sound economic sense.

Chapelizod sits just a few kilometres west of Dublin city centre, accessible by road along the south bank of the Liffey or via the Phoenix Park on the north side. The mill dam area near the present weir structure is the likeliest point of interest for anyone curious about the site's history. Commercial fishing here is long finished, and the weir is used today only by anglers. The Liffey at this stretch is relatively quiet, with a noticeably different character from the tidal, urban river further east, and the presence of the old dam is a useful physical reminder of how thoroughly this part of the river was once put to work.