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-
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
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 Indicator | 2023 Score | 2019 Score | 2015 Score |
|---|---|---|---|
| Ammonia-Nitrogen | 9.7 | 9.7 | 9.1 |
| Dissolved Copper | 7.7 | 7.6 | 7.0 |
| Dissolved Oxygen | 4.9 | 4.7 | 5.9 |
| E. coli | 7.6 | 8.0 | 7.6 |
| Temperature | 1.0 | 1.0 | 1.4 |
| Total Mercury | 4.0 | 4.4 | 4.0 |
| Total Phosphorus | 5.4 | 5.5 | 5.9 |
| Total Suspended Solids | 5.8 | 5.3 | 5.0 |
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
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 Indicator | 2023 Score | 2019 Score | 2015 Score |
|---|---|---|---|
| Bank Condition | 0.6 | 0.0 | 0.0 |
| Floodplain Condition | 5.2 | 6.7 | 6.7 |
| Large Wood | 2.4 | 2.6 | 2.0 |
| Riparian Integrity | 2.9 | 2.5 | 2.6 |
| Shallow Water Refugia | Not applicable | Not applicable | Not applicable |
| Stream Accessibility | 1.7 | 1.7 | 1.4 |
| Substrate Composition | Not applicable | Not applicable | Not applicable |
| Tree Canopy | 4.2 | 3.9 | 2.9 |
Hydrology Score: B-
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
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 Indicator | 2023 Score | 2019 Score | 2015 Score |
|---|---|---|---|
| Effective Impervious Area | 6.5 | 4.8 | 5.0 |
| Stream Connectivity | 5.5 | 5.6 | 6.7 |
Fish and Wildlife Score: D-
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
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 Indicator | 2023 Score | 2019 Score | 2015 Score |
|---|---|---|---|
| Birds | 4.4 | 2.8 | 3.9 |
| Fish | 1.0 | 1.1 | 0.9 |
| Macroinvertebrates | Not applicable | Not applicable | Not 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 partnerships 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.