A digger log imitates a naturally fallen tree in the stream that would help to create habitat diversity. As water plunges over the lower end of the log, it creates a pool which provides a deep, cool refuge for fish.
A ramp leading up to the log and made of flat rocks creates a riffle which is a productive feeding area for fish as well as a safe spawning location. A rock or log deflector pushes the flow to the pool side of the log. Digger logs also help to consolidate flow and restore a path of maximum depth (thalweg) and restore the natural meandering pattern.