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Tryon Creek is one of the major remaining free-flowing tributaries of the Lower Willamette River. The seven-mile stream flows southeast from Multnomah Village through Tryon Creek State Natural Area to its confluence with the Willamette River below Highway 43 in Lake Oswego.
The creek originates as a series of seeps and springs in Portland’s West Hills. These form tributary streams like Arnold, Nettle, Falling, Oak, and Park creeks. The whole Tryon Creek system is about 30 miles of streams. The watershed’s small, intact headwater streams provide natural flood control, recharge groundwater, trap sediments and pollution, recycle nutrients, create and maintain biological diversity, and provide summer flows to sustain the fish and wildlife in downstream rivers, lakes, and estuaries.
The Tryon Creek watershed covers over 4,000 acres. About 3,000 acres are in southwest Portland, and the remaining area is in the City of Lake Oswego and unincorporated Multnomah and Clackamas counties. About 21% of the watershed is parks and open space, including 667 acres of the lower watershed in Tryon Creek State Natural Area. Tryon Creek and its tributaries also run through Marshall Park, West Portland Park, and Maricara Park. The predominant land use in the watershed is single-family residential.
Like other parts of southwest and northwest Portland, the Tryon Creek watershed is characterized by a combination of steep slopes, soils that are slow to infiltrate rainfall, and impervious surfaces like streets, roofs and parking lots. These factors have had a severe impact on the streams, causing problems like erosion, channel incision, down-cutting of stream banks, landslides, and exposed sewer pipes that run along or across streams. About three miles of stream are in pipes or culverts, which can further exacerbate these problems.
All of the watershed is in the separated stormwater system, meaning that stormwater runoff flows through pipes, ditches and drainage ways, and discharges into streams. Water quality concerns include temperature, nutrients and sediment. Learn more about Portland’s stormwater management permit and requirements under the Clean Water Act and other regulations.
Despite these human impacts, Tryon Creek is a prime example of an important urban watershed that feeds the Willamette River and has many valuable natural resources that benefit Portlanders. Significant restoration and protection efforts are underway to protect the native salmon and steelhead still here. The Tryon Creek watershed provides shelter to abundant wildlife, including more than 60 species of birds that reside in the watershed for at least part of the year.
Find more detailed watershed characterization information about Tryon Creek on the Plans, Studies and Reports page.