A run is a section of river where the current is moderate to slow. A run can be identified by the head and tailout. The head of the run is where water gushes in from rapids, it is typically the deepest part of the run. The tailout is the end of the run, where the depth decreases gradually as water travels downstream. When fishing a river, it is best to focus your effort in runs.
When fishing for salmon and steelhead in British Columbia, anglers always work systematically from the head of the run to the tailout. When approaching a run, it is considered rude to start downstream from an angler who is already fishing. It is best to start upstream from the existing angler or ask for permission to start downstream from him or her.
Different salmon species would occupy different parts of the run, especially if many species are found in the same run. Chinook salmon typically occupy the deepest part of the run while coho salmon have a tendency to rest in the tailout.
When dry fly fishing for trout, it is common to start from the tailout of the run and cast your dry fly upstream. This tactic prevents trout from seeing your shadow and becoming spooked.