Tryon Creek Watershed

About the Tryon Creek Watershed

The headwaters of Tryon Creek spring from the ground in the West Hills of southwest Portland. The mainstem of the creek flows southeast for approximately seven miles from Multnomah Village. It continues through the Tryon Creek State Natural Area and reaches its confluence with the Willamette River below the Highway 43 crossing in Lake Oswego. Tryon Creek is one of the few major remaining tributaries to flow freely down from Portland’s West Hills.  

The watershed drains approximately 4,142 acres of land. Nearly 80 percent of the watershed is within the city limits of Portland. The rest falls within Multnomah County, Clackamas County, and the City of Lake Oswego. The primary land uses in the watershed are housing (mostly single-family homes), transportation (streets and roads), and parks and open space.

In the Tryon Creek watershed, sewer and stormwater pipes are separated. Sewer pipes carry sewage to the treatment plant, and many large sanitary sewer conduits, or pipes, run down Tryon Creek and its tributaries. Stormwater pipes collect the runoff from paved areas. Some pipes drain directly to the creek or its tributaries carrying pollution from the roads along with the runoff.

The watershed is within an urbanized environment. The major tributaries of Tryon Creek are Arnold, Falling, and Nettle creeks. The creek and its tributaries are typical of urban streams. Development has altered hydrology and flow patterns, and pollution has degraded water quality.  

How the Watershed Is Doing Today 

The most recent report card for Tryon Creek watershed uses data collected from the 2023 Watershed Health Index. Although there is room to do better, the most recent watershed report card scores were pretty good overall: 

• Hydrology – B
• Water Quality – B
• Habitat – B+
• Fish and Wildlife – D 

Review the Tryon Creek Watershed Report Card for more information.

Work We've Done to Improve Conditions

 To continue to improve watershed conditions, past and current projects focus on:

• Decreasing impervious surfaces and treating more stormwater runoff.
• Replacing and repairing aging sewer pipes.
• Removing culverts and other barriers to support salmon recovery, such as the SW Boones Ferry Bridge and Restoration project.
• Restoring and protecting natural areas and salmon habitat, such as the Tryon Creek Confluence Habitat Enhancement project.

In addition to past watershed restoration projects in the watershed, several sewer and stormwater projects have added green streets and bioswales to capture and treat stormwater runoff before it can flow to the creek or its tributaries. One example of this work is a terraced rain garden at the intersection of I-5, SW Barbur Boulevard, and SW 26th Avenue that collects and treats stormwater runoff from 24 acres of roadway. Prior to the project, rain running off these roads drained directly into Tryon Creek, carrying pollutants and causing high flows and erosion. Now, runoff flows into a forebay that captures sediment and pollutants before it flows through a series of rain gardens that slow the velocity and allow more pollutants to settle before the water reaches the creek. The rain garden project, a partnership with the Oregon Department of Transportation, improves water quality by slowing and treating 24 million gallons of stormwater each year and is the largest rain garden project to date in Portland.

Work We're Doing to Improve Conditions

Work to improve conditions continues:

• Projects to repair aging sewer pipes and better manage stormwater help protect water quality in the creek by keeping harmful bacteria and pollution out. Find information about all current Environmental Services projects.
• The Southwest Capitol Highway Project will include new sidewalks and bike lanes, new stormwater management facilities, and water system upgrades. These improvements will help to improve safety and mobility for all modes of travel, protect and improve water quality in the creeks in the watershed by treating stormwater, and update water supply infrastructure.
• The Basin 3-Tryon Headwaters projects will capture and hold stormwater runoff, reduce local flooding, and improve water quality before it discharges to Spring and Tryon creeks. 

Important Fish and Wildlife 

Tryon Creek has a low number of fish species found within it, but over 99 percent of the fish are native. Native reticulate sculpin and cutthroat trout are the two most commonly captured species, and rainbow/steelhead trout are occasionally captured. Currently, a culvert at Highway 43 significantly blocks fish from swimming up Tryon Creek to the prime habitat in the watershed. Environmental Services is working on a project to remove the culvert, which will open up the entire creek to fish.

Tryon Creek State Natural Area offers ample forest habitat for native birds. Pacific wrens, spotted towhees, black-capped chickadees, and Pacific-slope flycatchers are the most common species on stream surveys. Pileated woodpeckers can sometimes be seen in deeper forest haunts. Careful listening may reveal the presence of tiny Northern pygmy owls, which live year-round in the park. The barred owl is a recent arrival to the Pacific Northwest and the most common seen owl in Tyron and around Portland. Unlike most owls, barred owls are sometimes active during daylight hours. 

Typical mammal sightings include: 

• Beavers
• Blacktail deer
• Coyotes
• Opossums
• Raccoons
• Red foxes
• Skunks
• Squirrels

How to Experience the Tryon Creek Watershed 

The 658-acre Tryon Creek State Natural Area is a great way to experience a large, undisturbed portion of the watershed. Contact the park to take advantage of educational programs and guided hikes.  

How to Get Involved 

The Tryon Creek Watershed Council is active in protecting and enhancing the health and function of the watershed. Learn more on the council's webpage.

The Westside Watershed Resource Center inspires awareness and action on behalf of watershed health throughout Portland's westside. The center provides watershed resources including outreach and education, technical support and advice, a tool loan program, and project and partnership support. Learn more on the center's webpage.