Watershed FAQs

Metrics

• How big is the Tualatin Watershed?

  712 square miles (455,680 Acres)

• How long is the Tualatin River?

  The Tualatin River is approximately 83 miles long and flows from the eastern side of the Coast Range to the Willamette River.

• How many residents does the Tualatin River provide drinking water for?

  400,000

• What is the population of the Tualatin Basin (Washington County)?

  Population, Census, April 1, 2020
  600,372

  Population, Census, April 1, 2010
  529,710

  [PLACEHOLDER – 2025 census population data for Washington County needed]

People & Community

• What are the population demographics of Washington County?

  Based on Race and Hispanic Origin data from the 2025 Census:

  • 76.0% White alone

  • 3.2% Black or African American alone

  • 1.4% American Indian and Alaska Native alone

  • 13.8% Asian alone

  • 0.6% Native Hawaiian and Other Pacific Islander alone

  • 5.0% Two or More Races

  ---

  • 19.3% Hispanic or Latino

  • 59.5% White alone, not Hispanic or Latino

  We know this data doesn't show the full picture. Some of our neighbors - especially those facing housing issues, with mistrust of the government, or with mobility or language barriers - are harder to reach, and might be underrepresented in the data.

  For more information, please visit the Census website here.

• Who are the original inhabitants of the Tualatin River watershed?

  The Tualatin Band of Kalapuya were signers of the Willamette Valley Treaty of 1855, which ceded their homelands to the United States in exchange for certain rights and benefits. They were subsequently removed from their homelands to the Grand Ronde Indian Reservation where they became members of the Confederated Tribes of Grand Ronde. Their descendants live on as Tribal members today, carrying on the traditions and cultures of their ancestors, the original people of this land.

• What are the predominant uses of the land in the Tualatin Watershed?

  20% Urban

  30% Agriculture

  50% Forestry

• Who owns and/or manages the land?

  93% is privately or municipally owned

  5% is managed by the State of Oregon

  2% is managed by Bureau of Land Management

• What are the recreational opportunities?

  Many people enjoy canoeing on the Tualatin. The Tualatin Riverkeepers have a recreation guide.

  There are many public parks and trails found throughout the watershed. Hagg Lake is the most popular recreational area in the watershed and is open to boating, swimming, and fishing.
  

• What are the economic drivers in the Tualatin Basin?

  Agriculture; horticulture; forest products; food processing; high-tech, including software and electronics; sports equipment; and apparel.

Water Quality

• How do I find out the current flow of the river?

  The river’s flow is measured in cubic feet per second (cfs) and can be found at the US Geological Survey website

• What are the water quality issues?

  The Department of Environmental Quality issued Total Maximum Daily Loads for Dissolved Oxygen (excess oxygen-consuming organics and ammonia), Temperature, Bacteria, and Chlorophyll a (excess phosphorus) for the Tualatin Basin in August 2001.

Everything Else

• What type of climate does the watershed have?

  A Mediterranean climate with prolonged winter rainfall and summer drought.

  Mean winter air temperatures in the valley floor: 32º F to 63º F (0º C to 17º C)

  Mean summer air temperatures in the valley floor: 41º F to 83º F (5º C to 28º C)

  Rainfall varies from 100” to 120” in the Coastal Range to 48” to 36” in the valley (inches per year)

• What are the major tributaries?

  Tributary	Drainage Area (sq mi)	Length (mi)	River Mile of Confluence
  Scoggins Creek	45.1	19.2	60
  Gales Creek	77.9	23.5	56.8
  Dairy Creek	231	10.55	45
  ... West Fork Dairy Creek		25.6
  ... East Fork Dairy Creek		22.9
  Rock Creek	75.6	19.3	38.1
  Fanno Creek	32	14	9.3

• Where is the Tualatin River Watershed located?

  Most of the watershed is in Washington County, Oregon.  Small sections are also found within Clackamas, Tillamook, Multnomah, Columbia, and Yamhill counties

• What are the major cities are located in the Tualatin Watershed?

  • Banks

  • Beaverton

  • Cornelius

  • Durham

  • Forest Grove

  • Gaston

  • Hillsboro

  • King City

  • North Plains

  • Sherwood

  • Tigard

  • Tualatin

  • West Linn

• Are there species on the Endangered Species List in the Tualatin Basin?

  Winter Steelhead are listed as threatened.

• What types of wildlife can be found in the basin?

  Roosevelt elk, black-tailed deer, beaver and black bears are found in the Coastal Range.

  An estimated 5,000 Canada geese and 65,000 ducks winter in the basin.

  Bald eagles, osprey, herons, hawks and many more birds also live in the basin.