All you have to do is start talking about any system here and how to get to it and where to fish and there will be out rage. Kanaka Creek, Chehalis, Dewdney Slough, Alouette River and there's outrage. pretty much can do a search on here and you will see. Even now people are still salty about the Gravel pit. Its kinda funny because if you walk into any local Tackle store they will pretty much tell you ever secret spot and even draw you a map.
Still while i don't believe there are some secret spots there are definitely those less traveled like the Canyon on the Chehalis, Not very many people want to bushwhack then take a rope down a cliff but if you do it's pretty easy to limit out in the pools. Lately tho people have just been pontoon boating down.