Water Quality Improvement Project
Snohomish River Estuary:
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 transitioning from salt to 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
Water quality issues
Monitoring showed that the waters in the Snohomish Estuary system did not
meet water quality standards for dissolved oxygen. The Snohomish River Estuary
waters were placed on Washington State's 1996 Section 303(d) list of impaired
waters for ammonia and biological oxygen demand (BOD).
Why this matters
Ammonia (NH4+) is one measure of nitrogen, a nutrient that can
increase the growth of plants and algae in water. The presence of large
concentrations of ammonia in a stream or lake can create a large oxygen
demand. This demand is caused by the conversion of ammonia to nitrate,
called "nitrification". High concentrations of nitrate in wastewater
treatment plant effluent can cause algae to grow in large quantities.
Dead and decaying algae can cause oxygen depletion problems, which in
turn can kill fish and other aquatic organisms in streams.
Higher-than-normal levels of nutrients in the water can also lead to
changes in the water’s pH and clarity. In addition, increased algae and
plants can be ugly, create odor problems when they die, decompose and
interfere with recreational activities like boating and swimming.
Biological Oxygen Demand (BOD) is the amount of oxygen required by
aerobic microorganisms (organisms that need oxygen to survive) to break down
organic matter in water. It can be used to measure the amount of water pollution
in a water body.
What was done
Local governments and dischargers made changes and adjustments as
needed to divert effluent discharges to other appropriate locations,
improve wastewater treatment plants (WWTP), and update comprehensive
plans. Real-time water quality monitoring helped affected
facilities like the Everett facility to take interim storage measures in case the Snohomish River
approached critical flows before treatment upgrades were completed.
Snohomish River Estuary Total Maximum Daily Load: Submittal Report (Ecology
Snohomish River Estuary Dry Season TMDL Study Phase I - Water Quality Model Calibration (Ecology publication)
WRIA 7: Lower Snohomish
Watershed Information (Water web site)
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WRIA: #7 (Snohomish)
Snohomish River estuary
# of TMDLs: 3
TMDL approved by EPA
Department of Ecology
3190 - 160th Ave. SE
Bellevue, WA 98008-5452