In the case of normal timed coho it is a mix of East Fork Satsop and the natural stock trib by trib as fry plants in the many millions from Bingham supported the system. Chinook mixed bag as EFS stock went to the old upper Chehalis Hatchery / Hump to EFS, things moved around. Spring Chinook have had ZERO impact from supplementation. Chum, heaven knows as many eggs came in off the books / out of the watershed. As you purest are screaming one should remember this was in response to massive over harvest that brought on trying to reestablish the stock. Searun Cutthroat were planted all over but nothing like the Coho supplementation. Even the late Coho have been maintained with hatchery stocks.

So about the only true natural spawner is the Spring Chinook. The difference between the Chehalis and other systems is that the hatchery stocks were HSRG before it even was thought of. To much to go go into but through a series of mistakes and local visionaries drive, Chehalis hatchery and wild genetics are the same. Even the EFS stock was as much natural spawning as hatchery all about a short weir and high water.