That's a good question.
As there doesn't seem to be a mutual agreement on Columbia River use, I would suspect the river itself is fishable from bank to bank, from a boat, with an endorsement for Oregon licenses. I would also wonder if that includes tributaries, and how far upstream from the main river, from the Washington side of the river as well.
I suppose the main question you asked would have to be addressed to the Washington fish and game agency, whatever it's called. If you bring fish ashore in Washington, would you have to have a Washington license?
I know where I used to fish along the lower Colorado River on the AZ/CA state line, you needed a special use endorsement to fish the Colorado River from a boat. It also allowed you to fish the opposite bank from the shore of the state you were licensed in, plus some of the adjacent waters.
Of course, you could launch anywhere just for boating, as long as you were not fishing.
But you had to be careful there not to come ashore on any LCRIT reservation land. The crooked reservation game wardens would try and call you to the bank just so they could write you a summons if you didn't have a reservation license. Even though their authority did not include boats fishing the river.