Water Quality Improvement Projects
French/Pilchuck River Basins
The French Creek and Pilchuck River watersheds are part of the
Snohomish watershed. They help support important salmonid resources,
agricultural uses, and recreational activities. The Pilchuck River is
the largest tributary to the Snohomish River. Both watersheds are at the
outer boundary of tidal influence in the Snohomish River.
We are working with the U.S. Environmental Protection Agency and local
governments to determine the causes of too-warm temperatures which also affect
dissolved oxygen (DO) levels in both water bodies. Maintaining cooler water
temperatures will improve DO levels in the water, improving habitat for fish and
other aquatic life.
Water quality issues
French Creek and the Pilchuck River are considered core summer
salmonid habitat. This means their waters should not exceed 16°C (about
52°F) measured as a 7-day average daily maximum (7DADM) value. DO values
should not be below 9.5 milligrams per liter (mg/L).
Each water body is unique. For example, water quality and fish passage in
French Creek are significantly affected by the French Slough pump station and
numerous changes to the watershed in the floodplain area. The Pilchuck River
also experienced structural changes in its lower reaches and its upstream is
affected by municipal wastewater discharges from the city of Granite Falls.
Although the water temperatures and DO levels are thought to be good in the
Pilchuck River watershed for most of the year, high water temperatures and low
DO values have been recorded in a number of areas during the warm weather
months. Lower French Creek experiences similar problems.
What we have done
We began a combined temperature/DO total maximum daily load (TMDL) project
for the French Creek and Pilchuck River watersheds in 2012. During the initial
phases of the project, we worked with the EPA and a scientific consulting firm
to design the study. During the summer of 2012 we conducted extensive field
As part of the 2013 data assessment, we determined that some of the data
collected in lower French Creek was not usable because stream flows were
extremely low in that area. When looking at our Pilchuck River data, we
determined that additional flow and groundwater data was needed and we collected
that data during the summers of 2014 and 2016.
Status of the project
We are currently examining options on how to modify our technical approach
for modeling water quality in lower French Creek. We expect to complete modeling
of Pilchuck River water quality in July 2017. Afterwards, we will begin drafting
the Pilchuck River temperature/DO TMDL during the summer of 2017, and form an
advisory group in the fall. The advisory group will comment on study findings
and help develop the implementation plan. Following advisory group meetings, we
will gather public comment. We expect to complete modeling for the French Creek
temperature/DO TMDL by July 2018, with drafting of the TMDL and advisory group
Why this matters
Oxygen dissolved in healthy water is vital for fish and aquatic life
to "breathe” to survive. It is more difficult to transfer oxygen from water to
blood than it is to transfer oxygen from air to blood. Therefore, it is critical
that an adequate amount of oxygen is maintained in the water for this transfer
to take place efficiently and sustain aquatic life. Oxygen is also necessary to
help decompose organic matter in the water and bottom sediments as well as for
other biological and chemical processes.
Water temperature influences what types of organisms can live in a water
body. Cooler water can hold more dissolved oxygen that fish and other aquatic
life need to breathe. Warmer water holds less dissolved oxygen. Many fish need
cold, clean water to survive.
One way to cool water temperature is to shade the water body by adding or
retaining streamside vegetation.
Unless noted otherwise, the following are Ecology publications.
French Creek and Pilchuck River Temperature, Dissolved Oxygen, and pH Total
Maximum Daily Load Water Quality Study Design (Quality Assurance Project Plan)
Addendum to Quality Assurance Project Plan: French Creek
and Pilchuck River Temperature, Dissolved Oxygen, and pH Total Maximum Daily
Addendum 2 to Quality Assurance Project Plan: French Creek and Pilchuck
River Temperature, Dissolved Oxygen, and pH Total Maximum Daily Load
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