CogKnoSys

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Physical

Willamette River

The Willamette River flows 187 miles north through Oregon's Willamette Valley and joins the Columbia River at Portland.

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The idea

The Willamette River is a major tributary of the Columbia River, supplying 12 to 15 percent of the Columbia's flow. Its main stem is 187 miles (301 km) long and lies entirely in northwestern Oregon. It flows north between the Oregon Coast Range and the Cascade Range. The river and its tributaries form the Willamette Valley, which holds the capital, Salem, and the largest city, Portland. As of 2010, about 2.5 million people lived in the river's basin, about 65 percent of all Oregonians. Portland surrounds the river's mouth, where it meets the Columbia.

Plate tectonics first formed the river about 35 million years ago, and volcanoes and erosion later reshaped it. At the end of the last ice age, the Missoula Floods greatly changed its basin. People began living along the river over 10,000 years ago, and there were once many tribal villages near its mouth. Flood-laid soils and heavy rain made the valley one of the most fertile farming regions in North America and a goal for many pioneers on the Oregon Trail.

In the 19th century the river was an important route for boats, though Willamette Falls, just upstream from Portland, was a major barrier. The river and its tributaries support 60 fish species, including salmon and trout, despite dams, other changes and pollution.

Check yourself

Question 1 of 3

How much of the Columbia River's flow does the Willamette supply?

Pick one. The first pick counts.

Composition

what it's made of

  • Main stem — The 187-mile (301 km) main channel, entirely in northwestern Oregon.
  • Tributaries — Smaller rivers and streams that join it and together form the Willamette Valley.
  • Willamette Falls — A waterfall just upstream from Portland that blocked boat traffic.
  • Dams and reservoirs — More than 15 large dams in the basin, used for power, recreation and flood control.
  • Mouth at the Columbia — The river ends in Portland, where it joins the Columbia.

Connection

how it relates

Under Lower Columbia Rivers and Waterways

In place

  1. Portland, Oregonstrength 90 of 100

    Portland surrounds the river's mouth at the Columbia.

  2. Forest Parkstrength 60 of 100

    Forest Park stretches along hillsides overlooking the river, and many small streams in the park flow toward it.

Related

  1. Port of Portlandstrength 60 of 100

    In 1891, the Oregon Legislature created the Port of Portland to dredge and keep a shipping channel open from Portland to the Pacific.

Change

how and why it evolves

Past
Since 1900, more than 15 large dams have been built in the basin, 13 of them run by the U.S. Army Corps of Engineers. Part of the Willamette Floodplain became a National Natural Landmark in 1987, and in 1998 the river was named one of 14 American Heritage Rivers.
Now
In the 21st century, roads cross the main stem on about 30 bridges, and ferries carry cars and people across for a fare when the river allows.
Next
Pollution on the lower river and the effects of dams on fish are likely to remain major concerns for the river's future.

Knowledge you can walk. Read the idea, then step up, across or down.

Willamette River

The Willamette River flows 187 miles north through Oregon's Willamette Valley and joins the Columbia River at Portland.

See it on the map

Learn, discuss, create, buy or invest

The idea

The Willamette River is a major tributary of the Columbia River, supplying 12 to 15 percent of the Columbia's flow. Its main stem is 187 miles (301 km) long and lies entirely in northwestern Oregon. It flows north between the Oregon Coast Range and the Cascade Range. The river and its tributaries form the Willamette Valley, which holds the capital, Salem, and the largest city, Portland. As of 2010, about 2.5 million people lived in the river's basin, about 65 percent of all Oregonians. Portland surrounds the river's mouth, where it meets the Columbia.

Plate tectonics first formed the river about 35 million years ago, and volcanoes and erosion later reshaped it. At the end of the last ice age, the Missoula Floods greatly changed its basin. People began living along the river over 10,000 years ago, and there were once many tribal villages near its mouth. Flood-laid soils and heavy rain made the valley one of the most fertile farming regions in North America and a goal for many pioneers on the Oregon Trail.

In the 19th century the river was an important route for boats, though Willamette Falls, just upstream from Portland, was a major barrier. The river and its tributaries support 60 fish species, including salmon and trout, despite dams, other changes and pollution.

Check yourself

3 quick questions, instant feedback.