The Mayne River (Irish: Abhainn na Maighne),[1] is a small watercourse of northern County Dublin.

The river is in the jurisdiction of Fingal County Council and within the oversight of the Environmental Protection Agency.

Turnapin Stream rises in Harristown, passes through Dardistown, receiving two small tributaries, traverses the interchange of the M1 and M50 motorways, and crosses from Clonshaugh to Belcamp.

The Turnapin flows through the former Belcamp estate, where it receives smaller watercourses, and enters Balgriffin, where it merges with the Cuckoo Stream.

The Mayne passes under the Dublin-Belfast railway line at the Red Arches bridge and enters the former Baldoyle Racecourse lands.