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Stephens Creek Watershed

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Stephens Creek is a subwatershed to the Willamette River Watershed. It is one of the few remaining streams in Portland that flows mainly on the surface from its headwaters in southwest Portland to where it joins the Willamette River just north of the Sellwood Bridge.

What is a subwatershed?

A watershed is the area of land where all the rain and snowmelt drains to a common body of water such as a river or lake. Subwatersheds are usually made up of the smallest creeks, streams, and water bodies that drain to a bigger creek or stream that then flows into a larger river or watershed. In this case, Stephens Creek Watershed is a subwatershed to the larger Willamette River Watershed. 

A large watershed’s health is greatly impacted by the health of its subwatersheds. Healthy subwatersheds help to protect and improve the health of the larger watershed. Learn more about how healthy watersheds are important for people, fish, and wildlife.

About the Stephens Creek Watershed  

Stephens Creek begins at a steep ridge south of the center of the Hillsdale neighborhood in southwest Portland. The creek flows about two miles to join the Willamette River just north of the Sellwood Bridge. The creek drains a 754-acre watershed consisting of mostly residential neighborhoods with some areas of commercial development in the South Burlingame neighborhood along SW Barbur Blvd, part of the I-5 corridor, and the SW Taylors Ferry Road canyon.

The confluence of Stephens Creek with the Willamette River provides important off-channel habitat for fish in the Willamette River, including Chinook and coho salmon and steelhead trout (fish species protected by the Endangered Species Act). Off-channel habitat allows migrating fish to seek refuge from the larger river in sheltered spaces where they can find food and rest. Learn more about fish in Portland's rivers and streams.

The sanitary and stormwater systems that drain the Stephens watershed are separated. Stormwater runoff throughout the watershed is routed into pipes that discharge into Stephens Creek. Sanitary waste from homes and businesses is collected in sanitary sewer pipes and routed to the Columbia Boulevard Wastewater Treatment Plant for treatment. A large sewer trunk line carrying that sewage runs parallel to the creek as the creek flows through a forested canyon from SW Terwilliger Blvd and I-5 east past Fulton Park to SW Taylors Ferry Road.

How is the watershed doing today?

The largest challenge faced by this watershed is stormwater runoff. The watershed includes a stretch of I-5 and other busy transportation corridors like SW Barbur Blvd and Taylors Ferry Road. As rain runs off the hard surfaces of streets, parking lots, and driveways, it picks up pollution and carries that pollution often directly into the creek or its tributaries. As a result, water quality in the creek has been poor due to E. coli concentrations and pollution from runoff. 

In addition to pollution, the fast-flowing runoff causes significant increases in flow and volume of water in the creek during rain events. Many of the outfalls that drain roadways don’t slow the runoff before it enters the creek. Combined, these cause erosion of the stream banks and bed.

The watershed has moderate to steep slopes throughout, and the soils have very low infiltration rates. That also can increase erosion and limit stomwater management options that rely on infiltration.

A full watershed characterization is available in the Stephens Creek Stormwater System Plan. 

As a subwatershed to the Willamette, the Willamette River Tributaries watershed report card provides a good look at conditions in the watershed today. 

Work we’ve done to improve conditions

Improved stormwater management

Environmental Services has made meaningful improvements to manage stormwater in the watershed. 

  • The SW Texas St green streets and wetland enhancement projects, completed in 2007 and expanded in 2020, at the headwaters of Stephens Creek addressed localized flooding and improved habitat conditions. The 2020 wetland expansion provided additional floodwater storage. 
  • The 2015 Tryon-Stephens Headwaters Neighborhood Street Plan, a partnership with Portland Bureau of Transportation, provided for more connected street networks and improved stormwater management throughout the watershed.
  • Much of the watershed is privately owned property. New development and redevelopment projects on public and private property must now meet requirements of the City’s Stormwater Management Manual. These requirements help to protect the stormwater system and meet clean water goals.

Repaired and reinforced infrastructure to protect water quality

The 2008 Burlington Sewer Repair and Stream Restoration project repaired and protected the sewer trunk line that runs through the watershed. Erosion had exposed the sewer trunk. Repairs now prevent the sewage leaks that had increased E. Coli levels in the creek. In addition, the project restored and stabilized the creek’s banks and stream bed, repairing damage caused by erosion. The project also revegetated streambanks to shade and cool the water, removed invasive plants to allow for re-establishment of native species like Oregon ash, Western red-cedar, Pacific ninebark, Indian-plum, red-osier dogwood, and snowberry.

Find more information about previous projects along Stephens Creek on our watershed restoration and monitoring map. 

Work we’re doing to improve conditions 

The Stephens Creek Stormwater System Plan of 2013 has been guiding restoration and stormwater improvement work in the watershed. This long-range plan builds upon past investments and works toward a healthy stream system in the future. As outlined in the plan, future work will focus on slowing stormwater flows, treating runoff to protect water quality, improving habitat, adding trees and plants, and reducing flooding risks.

Important fish and wildlife

The forested areas and streams of the watershed provide important connections between the West Hills, the Ross Island-Oaks Bottom ecosystem to the east, Marquam Nature Park to the north, and Tryon Creek State Natural Area to the south. Tree canopy along Stephens Creek and its tributaries supports many native bird species. Robins, spotted towhees, and juncos are common sights along and near Stephens Creek.

The Stephens Creek confluence, where Stephens Creek joins the Willamette River, has been found to be the most salmonid species-rich place in the city. This is the only stream reach in the city where the four most common salmon or trout species have been observed (chinook, coho, cutthroat and rainbow/steelhead trout). Learn more about fish in Portland.

How to experience the watershed

The Stephens Creek Watershed includes several parks including the Stephens Creek Nature Park, A Park, and Fulton Park.

How to get involved

Many groups provide volunteer opportunities in the Stephens Creek Watershed. 

  • The West Willamette Restoration Partnership works to conserve and enhance the forests and natural areas of southwest Portland by forming an active coalition of engaged volunteers and organizations. The partnership aims to improve conditions that support diverse plants, animals, and people through land stewardship, volunteerism, and education.
  • The Westside Watershed Resource Center inspires awareness and action on behalf of watershed health in southwest and northwest Portland through a partnership between Neighbors West Northwest and Environmental Services.
  • West Multnomah Soil & Water Conservation District provides resources, information, and expertise to inspire people to actively improve air and water quality, fish and wild-life habitat, and soil health.
  • SW Trails promotes biking and walking throughout southwest Portland.
  • Support parks in the watershed through Portland Parks and Recreation Natural Areas Volunteer Stewardship. Find volunteer opportunities in the Stephens Creek watershed and throughout the city.