At the confluence of the Glendine River and the Blackwater, where one waterway folds into another, a fish weir was working the current long before it appeared on any map. A fish weir is essentially a fixed barrier or trap built into a river to channel fish into a confined space where they can be caught, and the Blackwater, running north to south through County Waterford, was clearly productive enough to support several of them at once.

By 1602, four weirs were recorded along the Blackwater between Ballynatray and Templemichael, and two of these were specifically tied to the manor of Ballynatray by 1604. The exact positions of all four are now uncertain, but one weir at least can be traced through two later documents. A Bateman map of 1717, held at the National Library of Ireland, marks a fish weir in this stretch of the river, and the first edition of the Ordnance Survey six-inch map, published in 1840, places one at the precise point where the Glendine River meets the Blackwater. Whether this is the same structure observed across a gap of more than a century, or simply the same general location reused as fishing grounds so obviously productive, the cartographic record at least establishes some continuity of interest in this spot. The association with Ballynatray manor in the early seventeenth century places these weirs within the broader context of landed estates managing and exploiting river fisheries, a practice with deep roots in medieval Ireland and considerable economic significance well into the modern period.