A U.S. Geological Survey five-year study of water quality has ranked
the Willamette Basin "among the most degraded" compared to 19
similar river basins studied throughout the U.S.
The Willamette River is the largest tributary to the Columbia River
below the Snake. It drains approximately 12,000 square miles of the most
densely populated part of the State of Oregon and empties into the Columbia
at Portland. It is a significant source of pollution to the Lower Columbia