River otter are accumulating contaminants at levels that are limiting their ability to reproduce. The Willamette River is a major source of pollutants to the lower Columbia River and contributes pesticides, bacteria, and, during high river flows, metals. The Columbia River above Bonneville Dam contributes the majority of metals, dioxins and related compounds. Most pollutants entering the lower Columbia River come from diffuse sources, such as urban and agricultural runoff. Examples include DDT which has accumulated in soil and is released through erosion, and PCBs which come from abandoned landfills and hazardous waste sites.
Some pollutants come primarily from industrial and municipal wastewater discharges.
These include dioxins and related compounds, and some heavy metals such as silver and cadmium. Bacteria levels in the river are generally not a health hazard for contact recreation except possibly along shorelines following rain storms. Bacteria comes from many sources including combined sewer overflows, urban storm runoff, municipal and industrial discharges, septic systems, marinas, boats and other diffuse sources such as agricultural runoff. Radionuclides were found to be below levels of concern. A computer model of diffuse pollution sources will be developed to assist the states in determining specific areas where pollutants enter the river.