Re: River's in Washington?
you probably aren't going to find any gold medal flyfishing in Western Washington. A GOOD trout in the western/puget sound rivers is a fish over 12" but there are a few places where you might have a chance. Unfortunately non of them are really "close" to you.
The Cedar River out of the Seattle area has a large number of over sized trout since it opened back up, after a very long closure, just a couple of years ago. It's a drive but it could be worth it.
Even further, the North Fork of the Stillaguamish, and the Main fork as well, are awesome for Sea Run Cutthroat which can grow to fairly good sizes.
Near Everett, the Snohomish/Snoqualmie/Skykomish system also offers trout and dollies as does the Skagit, but don't expect trophies.
My personal best was a 24" 5 1/2 pounder I caught from the main stem Stilly during this time of the year (The October Caddis hatch) on a #4 tied back october caddis riffle hitched and skated. Other good flies would be egg and/or flesh flies fished below salmon redds, fry and smolt flies after the spawn or during the smolt outmigration, and minnow/shrimp imitators in the river estuaries.
The real trophy fishing takes place on the east side of the state in the Yakima River, Crab Creek, and a few other places. Potholes and the seeps lakes are worth checking out but often they are beat to death by the bait fishermen. There are some trophy lakes in eastern washington as well, like Dry falls, Lenore, etc that are flyfishing only.
Pick up a fly fishing in washington book at any flyshop and read it religiously! it has a lot of fantastic information in it!