The Port of Portland is 104 miles up river from the Pacific Ocean and handles containerized freight and bulk cargo, including grain bound for export markets from Washington state, Oregon, Idaho and Montana.

The US District Court for the Western District of Washington had rejected the Northwest Environmental Advocates challenge to the study. The US 9th Circuit Court of Appeals upheld the lower court's decision that the Corps had taken a required "hard look" at the effects of the dredging project in its feasibility report and environmental impact statement.

Two judges on the three-judge panel of the San Francisco-based appeals court agreed, noting that the Corps had produced an "extensive examination of the project's cumulative, direct, and economic impacts."

"In this case, the Corps has demonstrated the hard look by performing exhaustive studies over numerous years, soliciting and accommodating input from stakeholders, and thoroughly reanalyzing areas of particular concern," Judge Barry Silverman wrote in the majority opinion.

Judge Betty Fletcher dissented, citing environmental concerns associated with deepening the Columbia River's shipping channel.

Fletcher wrote in her dissent that the Corps had failed to adequately study the effects of deepening, especially with regard to coastal erosion, release of toxic materials and salinity that could affect the health of the river and its already declining salmon run. "My bottom line is that the Corps has substantially more work to do," she concluded.

"The Columbia River is too important a resource for all of us to allow its misuse," Fletcher wrote. "Too much is at stake to permit the Corps to move forward with such incomplete and inadequate information."

Northwest Environmental Advocates was not immediately available to comment on the decision and whether it would ask for a review or if it would appeal the majority decision.