It is not a natural stream, nor a later industrial cut. It is a remnant of the medieval water supply system that once served Dublin city, and it has been quietly doing its job, or at least holding its line in the landscape, for centuries.

The feature appears simply as 'Watercourse' on the Ordnance Survey six-inch map of 1837, which is itself a sign that by that point it was already old enough to be treated as a piece of established geography rather than a named engineering work. The medieval Dublin city watercourse was a managed channel designed to carry freshwater into the city, a critical piece of urban infrastructure at a time when the supply and control of clean water shaped where people could live and work. This particular section follows the western edge of what is now the grounds of St. Paul's Church, a Passionist church whose congregation arrived in Mount Argus in the nineteenth century, and from there the channel continues northward to Grand Canal Harbour, where it meets the canal network that reshuffled Dublin's waterways from the late eighteenth century onward.

The area is accessible on foot from the Harold's Cross or Kimmage direction, and St. Paul's Church on Mount Argus Road is itself easy to locate. The watercourse boundary is not signposted or interpreted on site, so you are largely reading the landscape for yourself. It is worth walking the western perimeter of the church grounds slowly, looking for the subtle depression or channel that marks the old line. The logic of the route becomes clearer if you trace it mentally northward toward the Grand Canal, imagining water moving through a city that looked nothing like the one around you now. The 1837 OS map, freely available through the OSi historical mapping viewer online, is genuinely useful here, showing the feature at a moment when its medieval origins were already receding into background geography.