The U.S. Army Corps of Engineers has dredged the lower Columbia River since the 1860s to create a deeper shipping channel between Portland and the Pacific Ocean. 

The agency says the practice is necessary to support international commerce, but very few studies have been conducted on its ecological impact. Tribal leaders say dredging has contributed to the decline of lamprey, steelhead and other culturally significant species that rely on the Columbia estuary. Meanwhile, hydropower dams have caused a pileup of sediment in the mid-Columbia, slowing the river’s flow and raising water temperatures to dangerous levels.