Willamette River Tributaries Watershed Report Card

Information
Photo shows a scientist recording measurements next to a rapidly flowing, muddy stream in a wooded area.
This report card gives a snapshot of watershed conditions in Willamette River tributaries. The diverse area enjoys above average water quality and habitat scores but struggles with below average scores for hydrology and wildlife.

The following summary is based on data from the 2023 Watershed Health Index. The scores below are a snapshot of conditions across the entire watershed. Conditions can vary in smaller parts of the watershed.

The scores from 2019 and 2015, the first year Environmental Services released the report cards, are included.

Water Quality Score: B-

Water quality varies in Willamette tributary streams. In highly developed areas, stormwater sends pollutants like copper and total suspended solids to small streams like Stephens Creek. Tributaries near busy streets and highways also have poorer water quality due to street runoff. Other streams, such as Miller Creek in Forest Park, have much better conditions. But even streams in parks can have challenges. Erosion is a risk in parks due to steep slopes, human activities, and aging infrastructure. Erosion can cause soils and pollutants to wash into streams.

Preserving and protecting wetlands and forests like Forest Park and the River View Natural Area help to protect water quality and lower temperatures in streams. Green street infrastructure collects and treats stormwater runoff from streets and roadways keeping metals, and other pollutants from washing into local streams.

Scores for Water Quality Indicators

Graphic shows slider bars that represent data in table on water quality scores below.
Arrow shows 2019 score. Bar shows 2015 score.

Scores are on a scale of 0 to 10 with scores of 8 or higher meaning the indicator is properly functioning. A score of 3 or lower means the indicator is not functioning properly or provides little to no support for a healthy watershed. Find more information about the indicators and how to read the scores.

Water Quality Indicator2023 Score2019 Score2015 Score
Ammonia-Nitrogen9.99.99.9
Dissolved Copper5.45.15.6
Dissolved Oxygen8.78.68.7
E. coli6.38.66.1
Temperature4.04.55.6
Total Mercury1.81.01.7
Total Phosphorus6.16.36.6
Total Suspended Solids2.34.74.8

Habitat Score: B+

Southwest and northwest Portland have large, protected natural areas and forested neighborhoods. For this reason, scores are good for tree canopy, stream bank condition, and riparian area (the land with plants and trees alongside streams). Removal of invasive plants, which threaten forests in the Willamette Tributaries and other watersheds, and revegetation are important work we can do to protect and improve habitat.

Meanwhile, stream accessibility is poor because of the large number of piped streams. Culverts and pipes, like those on Miller Creek under Highway 30, block fish access between the Willamette River and Forest Park’s relatively healthy streams. Removing them gives fish access to prime habitat upstream in the park.

Scores for Habitat Indicators

Graphic shows slider bars that represent data in table on habitat scores below.
Arrow shows 2019 score. Bar shows 2015 score.

Scores are on a scale of 0 to 10 with scores of 8 or higher meaning the indicator is properly functioning. A score of 3 or lower means the indicator is not functioning properly or provides little to no support for a healthy watershed. Find more information about the indicators and how to read the scores.

Habitat Indicator2023 Score2019 Score2015 Score
Bank Condition10.09.810.0
Floodplain ConditionNot applicableNot applicableNot applicable
Large Wood6.05.04.8
Riparian Integrity8.27.98.1
Shallow Water RefugiaNot applicableNot applicableNot applicable
Stream Accessibility0.10.10.7
Substrate Composition8.67.46.5
Tree Canopy10.010.010.0

Hydrology Score: C-

Streets and other hard surfaces in the watershed create stormwater runoff. In some parts of the watershed, rain washes pollutants from streets into pipes that drain directly to streams. Fast-moving runoff can erode stream beds and banks. In addition, many of the Willamette's tributary streams that once flowed freely in the watershed were piped years ago to make way for development.

Better stormwater management overall will gradually improve these hydrology scores. Many of Portland's stormwater projects include adding new green streets to capture runoff and treat it before releasing it to a stream or allowing it to soak into the ground to replenish groundwater. 

Scores for Hydrology Indicators

Graphic shows slider bars that represent data in table on hydrology scores below.
Arrow shows 2019 score. Bar shows 2015 score.

Scores are on a scale of 0 to 10 with scores of 8 or higher meaning the indicator is properly functioning. A score of 3 or lower means the indicator is not functioning properly or provides little to no support for a healthy watershed. Find more information about the indicators and how to read the scores.

Hydrology Indicator2023 Score2019 Score2015 Score
Effective Impervious Area4.73.93.8
Stream Connectivity3.73.33.2

Fish and Wildlife Score: C-

Cutthroat trout and other fish live in streams in Forest Park, but the watershed’s fish score is low due to blocked 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. The park’s relatively healthy streams support insects, amphibians, and other wildlife.

Removing invasives plants and replanting with native plants helps support the region's native fish and wildlife. While work to make connections and create habitat between large forested areas like Forest Park and other natural areas helps support migratory animals. Overtime, such efforts will help improve these fish and wildlife scores.

Scores for Fish and Wildlife Indicators

Graphic shows slider bars that represent data in table on fish and wildlife scores below.
Arrow shows 2019 score. Bar shows 2015 score.

Scores are on a scale of 0 to 10 with scores of 8 or higher meaning the indicator is properly functioning. A score of 3 or lower means the indicator is not functioning properly or provides little to no support for a healthy watershed. Find more information about the indicators and how to read the scores.

Fish and Wildlife Indicator2023 Score2019 Score2015 Score
Birds6.24.85.4
Fish1.01.21.3
Macroinvertebrates5.85.65.9

In Summary

This watershed contains both large natural areas as well as dense, developed areas including central city and industrials. Perhaps, then, it is no surprise that its scores are just as divided. Work to restore and protect the tributaries are key to helping improve conditions in the mainstem for people, fish, and wildlife.

Read more about the Willamette River watershed.