It runs, mostly unculverted, from Harristown and Dubber near Dublin Airport, through Santry and Coolock, reaching the sea at Raheny, in a lagoon area inshore of Bull Island.

The lead branch can be found at the end of a small lane in the former Harristown Demesne, now cut off by new road development.

With the Dubber branch, it passes for most of its upper course out in the open, flowing through Sillogue Public Golf Course and the northern fringe of Ballymun; up to this point, the main channel is sometimes called Quinn's River.

In Coolock, the river forms a central feature in the valley which cuts through the district, and features a pond, sometimes Coolock Lake, and a small cascade, running past the Stardust Memorial Park, and through the grounds of Cadbury's Ireland, where there is an EPA monitoring station and a tumulus on its banks, just before it passes under the Malahide Road.

[1] The Santry passes the site of a covered holy well and enters Raheny near the beginning of Tonlegee Road, flowing alongside the Edenmore lands and past St. Joseph's Hospital.