It is barely two and a half metres wide and runs for roughly 400 metres in a north-east to south-west direction. To a passing eye it might look like little more than a damp field ditch, the kind of feature the midland landscape produces in abundance. The name, however, carries a rather grander claim.

Local tradition holds that this modest waterlogged groove is the remnant of a canal that once stretched approximately 2.4 kilometres, connecting the Bishop's Palace at Clonfert with Costello's Island on the River Shannon. If that tradition has any foundation, the feature would represent a genuine piece of ecclesiastical engineering, a private waterway linking a significant seat of church power to one of Ireland's great inland rivers. Clonfert itself has deep early medieval roots; St. Brendan the Navigator reputedly founded a monastery here in the sixth century, and the cathedral that now bears his name retains one of the finest carved doorways in the country. Whether the canal dates from that distant monastic era or from the later period of the bishops' residence is unknown, and no formal excavation or documentary evidence has been brought forward to settle the question. What survives on the ground is suggestive but inconclusive, a faint linear trace in wet ground that local memory has kept alive with a name and a story.