It is home to the largest
It is home to the largest non-delta river island in the world, Sauvie Island. Believed by 17th-century cartographers to be an estuary to the mythical Straits of Anian, its mouth was first observed in 1775 by Bruno de Heceta. The site of Hanford, where plutonium enriching was performed during the Manhattan project, lies along it, and dams along its length include Wanapum, Chief Joseph, and the Dalles. Pasco marks the point of confluence with the Snake, while the Willamette flows into it at Portland. For 10 points, what is this river, the second-largest in volume in North America, which forms part of the Oregon-Washington border?
It is home to the largest non-delta river island in the world, Sauvie Island.
{Columbia} River