The reason that Sockeye aren't native to the Cedar is because the cedar river did not used to flow into Lake Washington. Befor the locks where built, the cedar flowed into the Black River which was the outlet of the lake. It flowed in right below the outlet. The Black then flowed into the Green creating the Duwamish (sp) River. But the locks made the lake level go dow by twenty to thirty feet. If you look at the area around Renton, it is very flat and the Black River used to be very sluggish. So with the black River gone, the Cedar either flowed into the lake or was routed to the lake by man.

As most of us know Sockeye smolts, exept with a few exeptions, need to stay in a large lake for a year before they go to the salt. This is why they are not native to the Cedar River

Correct me if some parts of this are wrong as I got this from sketchy sources.