Martha Lake West Inlet, Stormwater Facility Improvement


Snohomish County Surface Water Management (SWM), a division of the Department of Conservation and Natural Resources, is planning a stormwater bio-retention facility within the grass strip owned by the Washington State Department of Transportation on the south side of 156th Pl SE. The bio-retention facility would benefit water quality for nearby natural habitats and people swimming, playing in, or using Martha Lake. It would treat stormwater flowing into an existing pipe under the grass strip, and is tentatively scheduled to begin construction around 2026.

Snohomish County is required to treat stormwater before it discharges into local water bodies like Martha Lake to comply with our Washington State Department of Ecology stormwater permits. An existing stormwater pipe under the grass strip at 156th Pl SE carries runoff flows from portions of unincorporated Snohomish County and WSDOT’s Interstate-5. The bio-retention facility would filter this stormwater through the soil and plants to remove pollutants. The clean stormwater would then drain into the existing storm system along Meadow Road to its current outfall at the west side of Martha Lake.  


The project is currently under Preliminary Design through 2024. Construction is currently planned for 2026.

Traffic Impacts

Construction would occur within the grass strip on the south side of 156th Place SE. During construction, flaggers would direct traffic along 156th Pl SE to maintain vehicle access while crews work. 


Snohomish County SWM has submitted an application to the Department of Ecology for grant funding for this project.