The source of the river is near Threlkeld, at the confluence of the River Glenderamackin and St. John's Beck. From there, the river runs westward, roughly aligned with the former Cockermouth, Keswick and Penrith Railway between Keswick and Penrith.
The river originates near Threlkeld, where it joins the River Glenderamackin and St. John's Beck. It then travels westward, generally aligning with the old railway line between Keswick and Penrith.