The Columbia runs from a lake in British Columbia, down through Oregon and eventually ends up in the Pacific Ocean.
The Columbia does not run through Oregon, it is the northern border of it from just south of Kennewick, Washington to the Pacific Ocean. The only US state that the Columbia actually flows through is Washington, which makes sense since the river starts in Canada, which is north of Washington, which is north of Oregon. Odd choice of verbiage.
Yes, I know. As I said, it’s the northern border of the state between the Pacific and just south of Kennewick, Washington. But it does not flow through Oregon, as only the south bank is ever on Oregon land.
The Columbia enters Washington from the north and then becomes its southern border all the way to the ocean. Being entirely surrounded by Washington for part of its course, it is accurate to say that the Columbia flows through Washington. Since the Columbia only interacts with Oregon as its northern border, beginning and ending its interaction on the same side of the state, it can not be said to flow through Oregon.
But wait! What about Sauvie Island and the Columbia slough? Are those not examples of the Columbia flowing through Oregon? Yeah, but not on the same scale and there’s nothing on Sauvie Island except for corn mazes and naked people.