In late fall, they close of the river and divert the flow of salmon up into a run. From, there the salmon are held until gravis. The spawn go in here:
They grow here, until about six inches, when they're released. There's a white spot on each back, where their dorsal fins are removed by state law. Helps to differentiate them from wild salmon. Imagine cutting the fin off of a couple of million smelt sized fish. Labor intensive.
The river they'll return up, three years hence.
And the quiet woods around.