Water Quality Improvement Project
Snohomish River Area:


The study area for this water quality improvement project included the Quilceda, Allen, Woods Creek, and the Sultan and Pilchuck River watersheds, which drain into the mainstem Snohomish River. Within the study area there are also four drainage systems controlled by pumping stations: French Creek, the Marshland, Deadwater Slough, and Swan Trail Slough.

The lower Snohomish River and its sloughs are an important habitat for adult and juvenile salmon to salt/fresh water before they migrate from one environment to the other. In addition to these waters, the lower four parts of the river, sloughs, and near-shore estuary are important juvenile rearing areas. Portions of the Skykomish and Snoqualmie river systems provide excellent spawning habitat for chinook, coho, pink, and chum salmon both in the main channels and tributaries. (See Study Area map)

Waterfall on the Snohomish River, Washington State.  Photo courtesy of Ralph Svrjcek, WA Department of Ecology.

Water quality issues

In October 1988 EPA released an interim strategy to regulate dioxin discharging from mills on the lower Snohomish River. Weyerhaeuser Paper Company in Everett showed up as a major source of dioxin on the river. Data showed measurable quantities of dioxin in the plant effluent, as well as in fish and shellfish samples taken near the mill. The data showed that existing effluent from this facility violated the dioxin water quality standard.

Why this matters

Dioxins are common by-products of a number of human and natural activities. These activities include combustion and incineration, forest fires, chlorine bleaching of pulp and paper, certain types of chemical manufacturing and processing, and other industrial processes. Dioxins are a concern because they are toxic contaminants that last a long time in the environment and can build-up in aquatic organisms, becoming more concentrated as they move through the food chain.

What was done

In June 1989 the Washington Department of Ecology listed eight pulp mills for violating water quality standards for the dioxin [2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)], including the Weyerhaeuser mill. Ecology developed a total maximum daily load (TMDL) for the Lower Snohomish River for TCDD, establishing a wasteload allocations (WLA) for dioxin pollution going into the lower Snohomish River. The WLA was included in a National Pollutant Discharge Elimination System (NPDES) permit for the Weyerhaeuser Paper Company, Everett Kraft Mill. EPA approved the TMDL in September 1992. Since the mill was closed at the time of this TMDL submittal, actual discharge levels were expected to be well below those authorized in the permit.

Technical information

Lower Snohomish River Dioxin TMDL (Ecology publication)

Related information

WRIA 7: Lower Snohomish Watershed Information (Water web site)


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Last updated March 2012
  Snohomish Watershed map


WRIA: #7 (Snohomish)
County: Snohomish

Water-body Names:
Snohomish River


# of TMDLs: 1

TMDL approved by EPA

Contact Info:
Ralph Svrjcek
Phone: 425-649-7165
Email: Ralph.Svrjcek@ecy.wa.gov

Northwest Region
Department of Ecology
3190 - 160th Ave. SE
Bellevue, WA 98008-5452