Upper Chehalis springers very likely evolved as a separate stock by being isolated by summer low flow and thermal barriers in the middle river that prevent chinook movement during the summer and fall before the rains come. Always has had a lot of poaching pressure, never very many fish spawning. Now we're apparently getting a spring chinook hatchery built by the Chehalis tribe, which will bring heavy fishing pressure on the wild component of the run as all hatchery programs do, and a proposed dam that is being promoted as a good thing because it will augment summer flows and reduce summer water temperature - the very environmental factors that maintain the spring run timing in the first place.