I'm not sure what the law is in Washington and the Oregon law is somewhat vague in identifying what streams are navigable but be aware that there are some selfish landowners in both states.
In the Tillamook, Oregon area there are several landowners that think they own all the river and you would be trespassing by merely drifting over it in your drift boat.
The usual means of defining bank access is the right to access a streambank up to the high water mark. However there are some landowners that feel differantly and WILL call the county sheriff if you are fishing on "their" river. Bear in mind that river access does not allow trespassing across privately owned land to get to the river.
The Association of North West Steelheaders is lobbying hard in the Oregon legislature to get more and more rivers designated navigable and we are making progress but we all need to be responsible and not trespass and litter.