UPDATED: October 2019

This is a summary of conditions in the Willamette Tributaries Watershed based on data from the 2019 Watershed Health Index. The scores are a snapshot of conditions across the entire watershed. Conditions can vary in smaller parts of the watershed.

Learn more about the Willamette Watershed

Program and Projects

This watershed has a lot of streets and other hard surfaces that create stormwater runoff instead of letting rain soak into the ground. In many areas, stormwater washes pollutants from streets into pipes that drain directly to streams. Fast-moving runoff can erode stream beds and banks.

Many of the streams that once flowed freely in the watershed today flow through underground pipes. The City is planning additional projects such as installing green street planters that will capture runoff and allow it to soak into the ground as soil and plants filter pollutants. Better stormwater management will improve these hydrology scores.

	Effective impervious area		3.9
	Stream connectivity		3.3

Water quality conditions vary greatly in Willamette tributary streams. Highly developed areas contribute a lot of stormwater pollutants like copper and total suspended solids to small streams like Stephens Creek. Runoff from streets and highways is a major source, and E. coli bacteria can come from sewer leaks or animal waste. Other streams, such as Miller Creek in Forest Park, have much better conditions. But even streams in natural area parks have challenges with erosion due to a combination of steep slopes, human activities, and aging infrastructure. This can cause solids and related pollutants to wash into streams.

The work Portland is doing to protect and improve streams, wetlands, and forests in places like Forest Park and the River View Natural Area help protect water quality. New green street planters and parking lot swales in commercial areas will reduce solids, metals, and other pollutants that wash into local streams. Planned projects, similar to a past project on SW Texas Street, will couple green street and rain garden projects with other infrastructure improvements, beginning in the Stephens Creek area.

	Ammonia-nitrogen		9.9
	Dissolved copper		5.1
	Dissolved oxygen		8.6
	E. coli		8.6
	Temperature		4.5
	Total mercury		1.0
	Total phosphorus		6.3
	Total suspended solids		4.7

Scores for tree canopy, stream bank condition, and the land and vegetation next to streams (riparian area) are good in many parts of the Willamette Tributaries watershed because of large protected natural areas and forested neighborhoods throughout southwest and northwest Portland. But habitat conditions are not the same across the whole area, and projects to protect forests, wetlands, and streams are important.

Invasive plants threaten forests in this and other Portland watersheds. Efforts to manage invasive plants, like Early Detection Rapid Response, are important to protect and improve habitat.

Stream accessibility is poor because of the large number of piped streams. Culverts and pipes, like those under Highway 30, block fish access between the Willamette River and Forest Park’s relatively healthy streams.

	Bank condition (hardening)		9.8
	Floodplain condition	Not applicable
	Large wood		5.0
	Riparian integrity		7.9
	Stream accessibility		0.1
	Substrate composition		7.4
	Tree canopy		10

Cutthroat trout and other fish live in streams in Forest Park, but the watershed’s fish score is low because of the many barriers that block fish access. Good tree canopy and protected natural areas provide habitat for birds and aquatic insects in this watershed. More than 104 species of birds have been identified in Forest Park, and the park’s relatively healthy streams support insects, amphibians, and other wildlife.

The City’s continued efforts to protect and improve connections between Forest Park and other natural areas on the west side, and improved stormwater management, will help improve these fish and wildlife scores.

	Birds		4.8
	Fish		1.2
	Macroinvertebrates		5.6

For more information about what we measure and where these scores come from, visit the About Watershed Report Cards page.

See some of what Environmental Services is doing for healthy rivers and streams on the Explore Portland’s Watersheds map.