Our Vision:
Together, we can help recreate a thriving stream full native plants and lifeforms. Arboretum Creek can be a living legacy for our children, a shining example of humanity living in harmony with nature, the core of a functional ecosystem, and an ongoing educational opportunity easily available to all King County residents.
Headwaters Project:
The Creek History:
Challenges for Arboretum Creek began in the 19th Century. The Arboretum Creek watershed was extensively logged. The removal of trees and vegetation would have reduced water retention while increasing silt, sediment, and scouring. Without the native vegetation to help moderate seasonal rainfall, human intervention would ultimately be required to manage storm surges. In addition, a trestle was built across Madison Valley to provide streetcar access.
During the next century, the challenges accelerated. The trestle was filled in and the rail line was converted to a roadway e.g. Madison Avenue. In effect, the new road became a dam which diverted the majority of Arboretum Creek. Topographic maps show that the Arboretum Creek Watershed would have originally collected water from as far south as Garfield High School.
With the opening of Montlake Cut in 1917 Lake Washington dropped nearly ten feet exposing an extensive shore of mud around the mouth of Arboretum Creek. For decades the exposed mud around Union Bay was used as a place to dump city refuse.
After the neighborhoods expanded in the 1920's much of the remaining stream water was diverted into underground piping and combined with the sewer. This Combined Sewer Overflow system still exists and on stormy days combines clean Alder Creek water with street runoff and our overflowing sewer system. The untreated water then flows directly into Montlake Cut.
When Lake Washington Blvd was created the resulting untreated road runoff was aimed directly at the stream and finally, even the small remaining balance of Arboretum Creek was diverted into an underground pipe. This diversion occurs below the Wilcox Bridge. This pipe routes the stream under the boulevard to minimize traffic disturbances. The outflow from this underground pipe is elevated above the final section of the stream and creates a barrier that fish are unable to cross.
The Result:
Even if fish could enter the stream at the north end, the small remaining water flow, particularly in the upper 1000 feet of the stream - starting just below the Japanese Garden ponds, comes to a complete stop during the warmer half of the year. During these months the creek becomes a series of stagnant pools, full of overheated water which nurtures an explosion of unwanted, and often invasive plants. Without water flow, there is insufficient oxygen to support native fish.
In 2017:
Friends of Arboretum Creek began working to reunite Alder & Alley Springs with Arboretum Creek, via what would become the Headwaters Project.
As part of the Arboretum Loop Trail Project, the upper portion of the Arboretum Creek stream bed was restructured including an initial planting of native vegetation along the shore. Additional growth and plantings will greatly benefit the stream habitat.
In 2020:
When the December flood brought water, oil & heavy metals into and through the Japanese Garden buildings. exotic plants and Koi ponds, the Headwaters Project expanded to intercept and sustainably clean the stormwater before returning it to Arboretum Creek.
In 2024:
Seattle Parks & Recreation formally took over leadership of the Headwaters Project with continued support from the Friends of Arboretum Creek.
In 2026:
The Headwaters Project completed the Parks 90% ProTech review, permit applications were submitted, funding exceeded 70% and July of 2027 became the goal for beginning construction.
The Current Opportunity:
The Headwaters Project plans to reunite Alder and Alley Springs with Arboretum Creek in 2027. This clean water is on the surface just uphill from the Japanese Garden. Re-uniting this clean spring water with Arboretum Creek will provide more than 40,000 gallons per day of year-round flow in Arboretum Creek.
Removing the clean spring water from the CSO will:
- Revitalize Arboretum Creek
- Reduce pollution in Montlake Cut
- Add cool water in Montlake Cut, which endangered salmon need
- Increase capacity in the King County Sewer, which will save money for King County Ratepayers
Redirecting & cleaning the stormwater will:
- Revitalize Arboretum Creek with more clean water
- Protect the Japanese Garden from flooding
- Sustainably reduce pollution in the Japanese Garden ponds, Arboretum Creek, Montlake Cut and all the way to the Salish Sea
- While also increasing capacity in the King County Sewer
The Future:
The Daylighting Project, after the Headwaters Project is completed, there are conceptual plans that include removing the lower portion of the stream from the underground pipe below Lake Washington Boulevard, near the north end of the creek.
This will allow fish, and encourage fish-eating birds, to return to Arboretum Creek and utilize the ecosystem the Headwaters Project helped to restore.
Multiple relevant stakeholder organizations have responded positively to this concept. Including:
- Seattle Parks and Recreation
- Arboretum Foundation*
- University of Washington Botanic Gardens*
- King County Wastewater Treatment Division
- Seattle Public Utility
- Seattle Department of Transportation
- Seattle Parks Foundation
* In 2026 the Arboretum Foundation and the UW Botanic Gardens combined to become the Seattle Botanic Gardens.
More information is available via our page entitled Latest News.