Both the Olympian and King 5 recently covered the weir being operated by the Nisqually Tribe. The purpose of the weir is to separate out hatchery chinook salmon from the wild run in hopes of helping establish a natural run of chinook.
From the Olympian story:
The portable dam, which includes traps and augers to lift the fish into holding tanks, is designed to capture every fall chinook salmon that has made it through a gauntlet of fisheries that stretches from Alaska to the river.
Once their migratory journey is halted, tribal crews sort the fish into two distinct groups: fish that were reared in one of the tribe’s two downstream hatcheries and fish that were born to naturally spawning parents upstream.…
“Given the history of chinook salmon in the Nisqually, restoring habitat is absolutely necessary before you start worrying about the mix of hatchery and natural origin fish on the spawning grounds,” Troutt said. “To develop a local stock, we need to be sure that only natural origin fish are spawning in the river. That is where the weir comes in.”
The weir is part of a much larger change going on in the Nisqually chinook management, including changes to harvest and recent increases in available habitat. David Troutt, natural resources director for the tribe, gave a talk a couple of years ago bringing all of the changes into focus: