This section of the valley is now blocked by a filling of glacial till, diverting the river south west, but the old course has been detected by drilling and echo-sounding.

The river rises on Paddaburn Moor in Kielder Forest and skirts the eastern edge of Butterburn Flow raised bog.

Peregrine falcons and ravens nest near the waterfall and derelict military structures, probably pump-houses supplying water for the Blue Streak rocket site at RAF Spadeadam, can be seen just upstream.

A 914-metre (2,998.7 feet) stretch of Wall, including two turrets and the impressive bridge remains, runs alongside the River Irthing at Willowford, linked by a new footbridge to Birdoswald Roman Fort.

[7] This crossing of the River Irthing marked a significant transition in the construction of Hadrian's Wall, emphasising the greater availability of building stone to the east.