Although generally shallow, the Deep River has depths of up to 6.5 metres (21 ft) in places.

The river's water quality is very good, fresh and low in nutrients.

The Deep River begins just west of Lake Muir about 50 km from the coast on the edge of the Yilgarn Plateau.

Lake Muir may, in flood, overflow into the Deep River catchment.

It flows through a valley between granite hills then wanders across the coastal plain, finally entering the Nornalup Inlet on the western side.