Water Quality Improvement Project
Sammamish River Basin
The Sammamish River watershed flows from Lake Sammamish to Lake Washington
in the Seattle metropolitan area. Because of the complexity of water
quality issues in this watershed, we will focus our efforts mainly on
the floodplain between the cities of Redmond and Bothell near Lake
Water quality issues
The Sammamish River is a highly modified water body with multiple
water quality problems. It was originally called Squak Slough and wound
about 30 miles through a large wetland complex to Lake Washington. When
the outflow of Lake Washington was rerouted to the Lake Washington Ship
Canal constructed in 1916, the level of the river dropped about 10 feet.
This led to the floodplain becoming fertile croplands. The river and
some tributaries were dredged and straightened to further improve
drainage for the new agricultural area and reduce flooding. In 1964, a
weir was installed near the outflow of Lake Sammamish to the Sammamish
Water quality in the Sammamish River is poor during summer months. Much of
the river lacks shade and large portions are heavily infested by the invasive
weed Egeria densa, or Brazilian Elodea. Along with relatively low flows that
occur during dry summer months, these factors contribute to the observed high
water temperatures and low dissolved oxygen levels in the river.
What we have done
Our study of the Sammamish River builds on earlier studies by local
governments and the Muckleshoot Tribe to help pinpoint problem areas and develop
solutions to improve the river’s water quality. Field work for the Sammamish
River temperature and dissolved oxygen Total Maximum Daily Load (TMDL) started
in late summer 2014. We prepared a
Quality Assurance Project Plan (QAPP) in early 2015 and collected data in
the summer of 2015.
The 2015 field work included two intensive surveys of groundwater and surface
waters where we evaluated water volume, temperature, oxygen levels, nutrients,
and several other water quality parameters at more than 20 locations. We also
performed several surveys of aquatic vegetation, including identification of
Brazilian Elodea. We installed two real-time telemetry stations to measure
dissolved oxygen and temperature continuously through summer 2015 through the
fall of 2016.
Status of the project
Field work for the study has ended. We expect to complete our data review and
quality control in 2017. Because of the complex nature of the river, we are
currently reevaluating the technical approach we will use to complete this TMDL.
We expect to have a better understanding of our next steps in the fall of 2017.
Although field work is completed and data review underway, we have not yet
assigned staff to build the water quality models that will provide the
scientific basis for the TMDL. That decision is likely to occur in spring 2018.
Why this matters
Oxygen dissolved in healthy water is vital for fish and
aquatic life to “breathe” and survive. Therefore, it is critical that an
adequate amount of oxygen is maintained in water to sustain aquatic
life. Oxygen is also needed to help decompose organic matter in water
and bottom sediments as well as for other important biological and
Water temperature influences the health of many organisms that live
in a water body. Cooler water holds more dissolved oxygen, which fish and other
aquatic life need to breathe. Warmer water holds less dissolved oxygen and makes
cold-water species like salmon more vulnerable to disease and predation. One of the most important ways to cool water temperature is to shade the water
body by adding or retaining streamside vegetation that blocks the sun.
Quality Assurance Project Plan: Sammamish River Temperature and
Dissolved Oxygen Total Maximum Daily Load Study Design (EAP publication)
WRIA 8: Cedar-Sammamish
Watershed Information (Water web site)
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