Trend Analysis Results for the McKenzie River at Coburg Road Upper Willamette Subbasin Upper Willamette Subbasin water quality is primarily influenced by extensive agriculture, although municipal and industrial point sources and urban non-point sources contribute to water quality conditions as well. The most upstream site on the mainstem Willamette River is at Oregon Highway 126 in Springfield. This site is about two miles downstream of the confluence of the Coast and Middle Forks of the Willamette River. Water quality variation at this site is dependent on water quality in the Coast Fork Willamette River, with dilution provided from the Middle Fork Willamette River. Water quality at this site is also influenced by Mill Creek, a small tributary adjacent to the monitoring site.
Mill Creek drains an industrial area in the City of Springfield.
Water quality is occasionally impacted during high and low flows by increases in total phosphates and biochemical oxygen demand, accompanied by high concentrations of total solids and fecal coliforms. After flowing through Springfield and Eugene and receiving the McKenzie River, the Willamette River becomes a braided stream that meanders northerly through the Grand Prairie. Non-point source pollution is evident, as relatively high levels of total phosphates and biochemical oxygen demand indicate runoff containing organic materials enters the river during the fall, winter, and spring. Occasionally, high levels of total solids and fecal coliforms are present during this time. Summer low flow conditions with high water temperatures stimulate the process of eutrophication.