Oregon's Willamette River, which runs through Portland, is one of the most polluted waterways in the U.S. Throughout its length, the river is lined with industrial plants and agricultural lands that have been using it as a dumping ground for decades. Sewage has regularly overflowed into its waters, and by the 1920s it was essentially transformed into an open sewer. It was listed as a Superfund site in 2000.
The problems are most exasperated lower on the river where all the contaminants collect. This area, roughly between Swan and Sauvie islands, is also along major industrial shipping channels.
Efforts to clean up Portland Harbor are complicated because Portland's sewage infrastructure remains compromised, and the site lies in a cumulative zone that collects pollution occurring all across the river's vast length. As a result, cleaning up the site provides only a temporary fix until the many pollution sources can be eliminated.