Roughly 70 metres from end to end and 25 metres wide, it sits quietly in a landscape crowded with older, more legible monuments, and its origins remain genuinely uncertain. It was still recognisable enough to be recorded on the 1837 Ordnance Survey six-inch map, shown as a rectangular pond fed by a water channel along its eastern side. Since then, post-1700 drainage works have cut across that same eastern edge, softening and partly obscuring what the pond's original margins would have looked like.

The uncertainty about who made it and when is part of what makes it interesting. Fish-ponds, typically engineered enclosures used to keep live fish as a reliable food source, were a common feature of both monastic and manorial estates throughout medieval Ireland and Britain. The pond at Tristernagh sits only 300 metres from the remains of an Augustinian priory founded in the thirteenth century, which makes a medieval origin plausible; religious houses frequently maintained fish-ponds to supply protein during fasting periods when meat was forbidden. But the same ground was later absorbed into the estate of Tristernagh House, built in 1783 on the site of the suppressed priory, and a Georgian landowner would have had equally practical reasons to maintain or construct such a feature. A medieval road and bridge lie immediately to the north and north-east, and Templecross church and its graveyard stand about 300 metres to the west, which gives the pond an unusually dense archaeological neighbourhood, whatever its own date turns out to be.