Delvin or An Ailbhine[3]: 2  is derived from Old Irish ailbine, possibly from ollbine, that is "great crime.

It passes along the northern edge of the village of Naul, where there are cliffs of around 20 metres, a 5 metre natural fall, and a small private hydro-electric plant on an artificial cascade.

[3]: 2  It passes under the M1 motorway, where is marks the county boundary, and later receives a final tributary and flows under a viaduct to enter the Irish Sea at Knocknagin,[3]: 2  at the southern end of Gormanston beach, south of Ben Head and some distance north of the village of Bremore, and the town of Balbriggan.

The main river body runs for about 18km, while tributary lines total at least 10km more.

[3]: 2 Trout fishing on these rivers takes place from February to September.