The Willamette River originates in the forested headwaters of the Cascade Mountains to the east and the crest of the Coast Range to the west. As the river descends from the mountains, it makes its way north through prime agricultural lands and three major metropolitan areas before meeting the Columbia River west of Portland. Over two million people live in the basin, clustered around its 11,000 miles of rivers and streams. The basin is the hub of the state’s population and economy with 70 percent of the state’s population, 75 percent of the state’s employment, and 12 percent of the state’s land area. The human influence on the river basin’s landscape is significant, creating some of the state’s most challenging water quality issues.
A 2009 study by the Department of Environmental Quality has found that land use is a critical factor influencing the health of the rivers and streams of the Willamette. Results of the analysis are based on a large amount of data that show the protection of fish, amphibians, aquatic insects and water quality is strongly dependent on streamside vegetation. Trees, shrubs and groundcover along streams provide a number of functions that protect the health and biological conditions of the streams.
Agricultural use and urbanization put a considerable strain on the health of the rivers and streams throughout the basin. Forestry also affects stream health. The study analyzes the status of the river, including its 12 sub-basins, using chemical, habitat and biological measurements of aquatic health. It finds the most prevalent and significant problem is stream temperatures that are too warm for salmon and other aquatic species. Other major problems are caused by human disturbance, and a reduction of trees and shrubs. The report finds that the restoration and maintenance of native streamside vegetation may be the best and most practical solution to several problems.