We are excited to publish the first annual data report for our Longfellow Creek Community Water Quality Monitoring Program!
Powered by a group of dedicated volunteers, the first year of monitoring generated over 300 tests and 125 bacteria samples. DNDA has done forest restoration work in the Longfellow Creek watershed for nearly a decade, and many of our water quality monitoring locations are located adjacent to current or historic DNDA restoration sites. In 2025, four sites along Longfellow Creek and two additional sites within the watershed were tested monthly.
Data collected thus far illustrates a definite need for continued testing. Multiple sites showed high water temperature, low dissolved oxygen, and significant variability in E. coli concentration; results consistent with historic findings from King County and the Washington Department of Ecology.
The program’s goals are to increase awareness of Longfellow Creek’s water quality issues and catalyze urban creek stewardship within the community. Data collected through this program is publicly accessible and shared with relevant stakeholders, with the hope that it can support more informed and evidence-based decision-making in the future.
One of the few remaining salmon-spawning streams in Seattle, Longfellow Creek flows through the highly urbanized Delridge neighborhood, where impervious surfaces generate significant stormwater runoff that degrades overall creek health. Spanning 4.2 miles, the creek drains approximately 2,700 acres, with nearly one-third of its flow routed through underground pipes. The creek ultimately drains into the Duwamish River and Puget Sound.
Despite its designation as salmonid spawning, rearing, and migration habitat with regular Coho returns, habitat quality in Longfellow Creek is severely limited by poor water quality, altered hydrology, and channelization. The creek is currently listed by Washington State as an impaired waterway for failing to meet water quality standards for temperature, dissolved oxygen and bacteria (E. coli and fecal coliform).
Testing parameters were selected based on historic monitoring data, key parameters of concern identified by the Washington Department of Ecology, and Global Water Watch testing methods. We partnered with the Sno-King Watershed Council to train volunteers and build our program, which is now part of a large network of community water quality testing programs across the country.
Findings from 2025 establish an important baseline for understanding current creek conditions in comparison to historic data collected by King County and other groups. Trends from 2025 testing illustrate that water temperature, dissolved oxygen, and E.coli measurements still fall outside of State standards for salmonid streams.
Dissolved oxygen and E. coli values violated state standards more significantly than water temperature, with dissolved oxygen levels falling to 50 percent of state standards between June and September at some sites and nearly all sites measuring low dissolved oxygen levels all year. Tests from only one site, Dragonfly Garden and Pavilion, demonstrated dissolved oxygen levels within state standards in 2025.
E. coli levels were also highest during the warmer months. Values fluctuated greatly throughout the year and across sites, so more testing should be done before determining how, or if, site location affects E. coli concentration.
Although we have only completed one full year of testing, data collected thus far illustrates a definite need for continued testing. Multiple sites along Longfellow Creek are still measuring high water temperature, low dissolved oxygen, and significant variability in E. coli concentration; these results are consistent with historic findings from the Washington Department of Ecology and King County.
If you want to learn more about our results from 2025, check out our first annual data report here!
For more information about the Longfellow Creek Community Water Quality Monitoring Program, contact Environmental Engagement Coordinator Louisa Keyani at louisa@dnda.org.
