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Columbia Slough Watershed Report Card

Information
Photo shows a still body of water with lots of trees and plants along the banks and patches of green aquatic plants along the surface. Sunlight glistens on the water.
This report card summarizes conditions in the Columbia Slough watershed. Highly developed, this watershed faces challenges in improving its habitat and fish and wildlife scores. Thanks to decades of investment, water quality and hydrology scores have improved.
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The following summary is based on data from the 2019 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 2015, the first year Environmental Services released the report cards, are included.

Water Quality Score: B-

Investments over the last 20 years have improved the Columbia Slough’s water quality. Stormwater treatment in the Columbia Slough watershed remains a priority. We can improve water and sediment quality by reducing pesticides, polychlorinated biphenyls (PCBs), and toxic organic compounds. We can increase vegetation along the banks and restore riparian buffers. By returning shade, we can reduce water temperature and provide other benefits.

Scores for Water Quality Indicators, 2019 and 2015

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 Indicator2019 Score2015 Score
Ammonia-Nitrogen9.79.1
Dissolved Copper7.67.0
Dissolved Oxygen4.75.9
E. coli8.07.6
Temperature1.01.4
Total Mercury4.44.0
Total Phosphorus5.55.9
Total Suspended Solids5.35.0

Habitat Score: D-

Roads, businesses, industries, homes, and port facilities dominate the watershed. This level of development leads to poor overall habitat scores. However, the watershed also has regionally significant habitat resources that are protected as natural areas, including Smith and Bybee Wetlands, Vanport Wetlands, and Big Four Corners Natural Area.

The poor riparian score is due to the history of development right up to the slough banks. This leaves little to no buffer of plants and trees. Since 1995, we have worked with private property owners to restore riverbank and revegetate City-owned natural areas. These efforts have had a positive impact, but we have more to do.

Scores for Habitat Indicators, 2019 and 2015

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 Indicator2019 Score2015 Score
Bank Condition0.00.0
Floodplain Condition6.76.7
Large Wood2.62.0
Riparian Integrity2.52.6
Shallow Water RefugiaNot applicableNot applicable
Stream Accessibility1.71.4
Substrate CompositionNot applicableNot applicable
Tree Canopy3.92.9

Hydrology Score: C+

Over half of the Columbia Slough system is highly altered. Levees and pumps control flow, drainage, and flooding. To improve hydrology, we can reduce impervious surfaces and better manage stormwater. The Mason Flats Wetland Enhancement project, for example, manages runoff from more than 600 acres of development. New stormwater management projects that let runoff soak into the ground and replenish groundwater will help improve the impervious area score, water quality, and habitat.

Although levees block migrating fish access to half of the slough, most of the waterways within the leveed area are open with very few piped sections.

Scores for Hydrology Indicators, 2019 and 2015

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 Indicator2019 Score2015 Score
Effective Impervious Area4.85.0
Stream Connectivity5.66.7

Fish and Wildlife Score: F

The watershed is at the junction of the Columbia and Willamette rivers, a key area along migratory routes for birds and fish. The slough watershed is home to 170 species of birds and 29 species of fish, including salmon and steelhead that use the lower slough while migrating to the ocean. Monitoring in the lower slough shows salmon from both the Willamette and Columbia rivers use the area.

Native fish species reside in the middle and upper sloughs. While a few large natural areas support fish and wildlife, inadequate riparian buffers and tree canopy limit overall conditions. Projects to improve habitat and water quality will help increase abundance of fish and wildlife. For example, Environmental Services installed 35 engineered log jams along nine miles of the lower Slough to improve habitat for small migrating salmon. The slough’s quiet waters offer endangered steelhead, coho, and Chinook salmon refuge from strong currents and predators in the Willamette and Columbia rivers on their migratory routes.

Scores for Fish and Wildlife Indicators, 2019 and 2015

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 Indicator2019 Score2015 Score
Birds2.83.9
Fish1.10.9
MacroinvertebratesNot applicableNot applicable

In Summary

The Columbia Slough is healthier and more vibrant than it has been in a century. Water quality, in particular, has improved greatly thanks to 20 years of focused investment. Public-private partner-ships and volunteer efforts to restore riparian areas along the slough offer hope for improving fish, wildlife, and habitat scores in the future.

Read more about the Columbia Slough watershed.