Keep in mind the Cedar never entered Lk. WA. That was man made during the ship canal project 1912-16 ish. I believe the Cedar ran into what was the "Black River", now culverted in it's entirety. The Black drained the South Lk. Wa area, then ran into the Green R. Back then, I'm sure Salmon and Steelhead populated the Black and Cedar via the Green. Leave it up to man to f all that up.
The Sockeye were introduced in the 30's after the Cedar was diverted into Lk WA. Sockeye need a lake river system to survive. The success of the Lk. WA Sockeye was because of the fertile/polluted lake. The 90's into 2000 Lk WA was cleaned up such that the Sockeye food supply, zooplankton, diminished. This, along with an increase in predators has impacted the Sockeye population what it is today. Even with the hatchery in operation the numbers will never reach what they used to be. Either the 300k return threshold to sportfish for them in the lake needs to be reduced, or we will never fish for them again. Tribes are happy. They still get to harvest a historically introduced fish not native to the system. The introduced Sockeye was a good idea, but you need a dirty lake for them to thrive. My buddy grew up in Renton through the 50's and told me stories how their dad used to wash them off with a hose after swimming in the lake. That's how good it was for the Sockeye. Or, how bad it was for swimmers.