Environmental Stewardship

Smith Island Estuary Restoration

In 2018 Snohomish County and the City of Everett completed construction of the Smith Island Estuary Restoration project. The project restored tidal influences to about 378 acres of land which had been separated from Union Slough since the early 1900s. Reintroduction of tidal influences is expected to create estuary habitat within the site. The restoration of estuary habitat within the Snohomish River Basin is a high priority for a number of regional salmon recovery efforts.

See the Snohomish County Smith Island Estuary Restoration page for more information about the project and its regional significance.

Check out the before and after story map: Smith Island Estuary Before and After. Use the slider bar to switch between a 2015 pre-project aerial photo and an aerial image taken in the fall of 2018, shortly after completion of the project. Additional aerial imagery will be available on the Map Everett interactive map by turning on the “Project_Site_Imagery” layers.

The City’s portion of the project is located north of City’s sewer treatment lagoons and adjacent to the Smith Island/Union Slough Restoration site as shown in Smith Island Estuary Restoration Map (PDF). The South Smith Island Diketop Trail is open.  The trail is a large loop of south Smith Island that starts at Langus Riverfront park, extends south along the Snohomish River to the south tip of the island, and then heads north along Union Slough and the multiple restoration projects up to 12^th Street NE.  At 12^th Street NE the trail goes over SR529 with an overpass to the grass diketop along the Snohomish river and back south again to Langus Riverfront park.

Project permits required extensive monitoring of the project site to demonstrate that the project met its restoration goals. View or download the Smith Island Estuary Restoration Monitoring Reports, listed by year:

• Year 1 (PDF)
• Year 2 (PDF)
• Year 3 (PDF)

Advance Mitigation Credits

The City’s portion of the project was designed as an Advanced Mitigation site. As monitoring of the site demonstrates its success in restoring estuary habitat the project will generate habitat credits which can use to offset future wetland and habitat impacts caused by City projects. Unlike the credits generated by the Smith Island/Union Slough Restoration project the credits generated by the Smith Island Estuary Restoration project are not limited to use for impacts on Smith Island. The credits can be used to offset unavoidable wetland and habitat impacts caused by City projects anywhere in the Snohomish River Basin. Once fully developed the site is anticipated to generate approximately 35 acres worth of credits.  As credits begin to be generated and debited a ledger of available credits will be posted here.

Silver Lake Monitoring

The City has collected water quality samples at various depths at one station at Silver Lake since 1989. View the 2023 Silver Lake health report.

Sampling

The lake is sampled for the following:  chlorophyll a, total and ortho-phosphorus, ammonia, nitrate-nitrite, iron and silica. Field measurements collected are temperature, dissolved oxygen and Secchi depth.

The purpose of the City’s monitoring of Silver Lake is to look at water quality trends over time as related to nutrients and lake productivity.

Lake productivity and nutrients

The productivity values or trophic state values have varied from year to year, but most have been in the oligotrophic range (below 40). The sampling data suggest that Silver Lake’s trophic state has not declined since monitoring began in 1989.

What does oligotrophic mean? Low biological productivity. Oligotrophic lakes are very low in nutrients and algae, and typically have high water clarity and a nutrient-poor inorganic substrate. Oligotrophic water bodies can produce and support relatively small populations of living organisms (plants, fish and wildlife). If the water body is thermally stratified, hypolimnetic (deep water) oxygen is usually abundant.

Milfoil removal at Silver Lake

Silver Lake has been plagued by excessive growth of an invasive macrophyte, Eurasian milfoil. Unlike algae, rooted aquatic plants like milfoil obtain their nutrients primarily from the lake bottom sediment. The City hires divers to remove milfoil by hand from the lake nearshore swimming beach annually. In recent years, milfol has not been observed in the nearshore zone monitored by divers.

Other resources

Click on the links below for more information:

• Snohomish County Surface Water Management, Silver Lake
• Thorton Tributary drains into Silver Lake and has been sampled during baseflow conditions quarterly, view baseflow data 
• Washington State Department of Health Fish Consumption Information  
• Snohomish Health District, Beaches, Lakes, and Rivers

Stream Baseflow and Benthic Monitoring 

The City has performed surface water monitoring of local creeks for more than 20 years. Staff perform monitoring to provide basic information on baseflow water quality. Most creeks are sampled seasonally (4 times per years during baseflow conditions). The City also collects macroinvertebrates samples from 8 creeks one time per year in late summer. For sampling locations see the Baseflow Sampling map (PDF). Data for these locations can be found in the Waterbody Monitoring Data sections of the Surface Water Comprehensive Plan basin chapters.

For questions about the stream baseflow monitoring or benthic monitoring contact Dana Zlateff, Surface Water Compliance Specialist, email or 425-257-8927.