I stopped in Olympia this afternoon for a lovely lunch and a little jaunt around a park that has a salmon hatchery.
That concrete wall hides a ladder for the salmon to run up, with a series of pools, kind of like locks, that the salmon can rest in.
This is where they end up. See their little backs poking out of the water? They put ladders like this besides rivers to make the run easier, or next to dams so that the salmon can get up where human engineering would otherwise prevent it.