[3] Slate River rises near Ballynafagh Lake in Prosperous and flows southwest, passing under the R403 road at Graigues.

It continues westward parallel to, and north of, the Grand Canal.

The Slate passes under the Grand Canal via the Derrymullen aqueduct and is bridged by the R415 at Littletown.

The Slate River continues through Ballyteague Forest and passes by the Lullymore Heritage and Discovery Park on the Bog of Allen.

Northern pike, European perch and brown trout are common.