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Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Avenue, Suite 1000, Portland, OR 97204

Willamette River Basin

Willamette Basin Map

Oregon's Largest Watershed

For more information, visit the Willamette Basin Explorer.







The Willamette River Basin is the largest watershed in the state, covering more than 11,500 square miles. Thirteen major tributaries join the Willamette River as it stretches nearly 300 miles from its headwaters at Waldo Lake in the Cascade Mountains southeast of Eugene to the confluence with the Columbia River at Kelley Point. Along the way it passes through forest, farmland, small towns, and large cities.

Portland occupies only a small fraction of the river's drainage basin, about one-half of one percent, but it is the most urbanized area. The 17 river miles that pass through the city, from just south of the Sellwood Bridge to the Columbia River confluence at Kelley Point, constitute less than 7 percent of the river's length but comprise the most heavily used river reach in the entire state.

By the Numbers

  • 11,460 - Basin size (square miles)
  • 12th - Rank among US rivers (in volume)
  • 16,000 - Miles of streams in the basin
  • 44,000 - Miles of roads in the basin
  • 100 - Number of cities in the Willamette Valley
  • 70 - Percentage of Oregon's population in the valley

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