Water Quality Improvement Project
Palouse River Mainstem
The Palouse River enters Washington State near the town of Palouse
and flows west through a variety of terrain until it meets the Snake
River downstream of Hooper and the Palouse Falls. When you take into
account the drainage areas of all of the Palouse River tributaries, this
is one of the largest watersheds in Washington. Therefore, much of
Ecology’s initial water quality work has focused on the main stem
Palouse River and tributaries known to be impaired. The studies
described on this page are limited to the Palouse River, Rebel Flat
Creek, and the mouths of several other tributaries.
The South Fork Palouse River is a major tributary with multiple water quality
problems. Please see the South Fork Palouse River
Project page for more information on studies in this sub-watershed.
Water quality issues
The Palouse River is listed as impaired for dissolved oxygen, pH,
fecal coliform bacteria, temperature, and several
historical pesticides and PCBs. To learn more about the importance of these various
parameters, please see our water quality impairments page.
Status of the projects
Due to the size of the watershed and multiple water quality
impairments along the Palouse River, water quality improvement efforts
are separated into several individual projects. While the studies and
reports for each of these projects may be separate, implementation
activities to address one water quality problem also typically help the
other issues. Project summaries with links to more specific information
North Fork Palouse River Dissolved Oxygen and pH
The most recent study of the Palouse River examined dissolved oxygen and pH,
which are influenced by excess nutrients. The current efforts on dissolved
oxygen and pH only address the North Fork Palouse River (from the state line to
the river's confluence with the South Fork Palouse River in Colfax). Data
for this study was collected in conjunction with the bacteria study, and
intensive surveys were conducted in Summer 2007 and 2012. Data on the
North Fork Palouse River indicates that at times it has too little oxygen and
the pH is too high to support healthy fish and other aquatic life. The
concentrations of nitrogen and phosphorus in the river affect the amount of plant and algae growth
in the water. Plants affect both oxygen and pH levels in water bodies through
photosynthesis and respiration.
A water quality
improvement report describes the dissolved oxygen and pH problems in the North Fork
Palouse River and what needs to be done to bring the river back into compliance
with water quality standards. This report was reviewed and approved by the
Environmental Protection Agency (EPA) in December 2016. For more information see the
Palouse River Area: Dissolved Oxygen and pH webpage.
Dissolved oxygen and pH impairments on the lower Palouse River,
downstream of the confluence with the South Fork Palouse River, are
outside the scope of this project and be addressed in the future.
Another study, also initiated in 2007, examined contributions to high water
temperature. Water temperature affects the health
and distribution of fish and other aquatic life. This study ran from May -
October 2007, during the time of year when the water was most likely to be
report on the study findings and an implementation plan to address the
issues contributing to human causes of high water temperature was completed and
submitted to the Environmental Protection Agency for their review and approval
on July 17, 2013. EPA approved the report on November 5, 2013.
(Excluding the North Fork Palouse River – see see North Fork Palouse River Fecal Coliform Bacteria)
A study, initiated in 2007, examined the levels and distribution of fecal coliform bacteria throughout the
watershed. Fecal coliform bacteria come from the intestinal tracts of humans and warm-blooded animals. It can indicate the presence of human and animal waste
which may carry disease-causing organisms. The Palouse River and Rebel Flat Creek are impaired by fecal coliform bacteria. This study ran from May 2007-May
2008 and a report and implementation plan outlining actions to reduce bacteria were published in December 2010. EPA reviewed the report and approved it March 2011.
Note: The portion of the Palouse River from the Idaho border to Colfax (also known as the North Fork Palouse River) was addressed under the
North Fork Palouse River Bacteria TMDL.
Previous studies found high levels of historical pesticides and PCBs in Palouse River fish. So, in May 2005 Ecology began the first study to examine
several toxins in the Palouse River. A TMDL report
detailing how the Palouse River will achieve water quality standards for PCBs
and dieldrin (the only chlorinated pesticides still above standards) was
completed and submitted to the Environmental Protection Agency (EPA). EPA
approved the TMDL on November 9, 2007.
The first project initiated in the Palouse Watershed was the development of a
plan to address fecal coliform bacteria in the North Fork Palouse River. This
effort was lead by the Palouse Conservation District (PCD). The PCD provided
their monitoring data and implementation plan to the Department of Ecology to
develop into a TMDL to comply with the Clean Water Act.
Cow Creek is also listed as impaired for dissolved oxygen, fecal
coliform bacteria, and temperature. An evaluation of the on-going implementation activities on
Cow Creek determined that these activities should address these water quality problems.
Therefore, these impairment listings have been reclassified as
category 4b (addressed by a
pollution control plan) on Washington's Water Quality Assessment.
Pleasant Valley Creek is listed as impaired for fecal coliform
bacteria and pH. This stream is outside the scope of this project and
will be addressed at a later date.
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WRIA: #34 (Palouse)
Rebel Flat Creek
Fecal coliform bacteria
# of TMDLs:
DO and pH - 28
Fecal Coliform - 3
Temperature - 2
Toxins - 4
Toxins - TMDL approved by EPA, has implementation plan.
Fecal coliform - TMDL approved by EPA, has implementation plan.
Temperature - TMDL approved by EPA, has implementation plan.
Dissolved Oxygen and pH - TMDL approved by EPA, has implementation plan.
Department of Ecology
4601 N Monroe Street
Spokane, WA 99205-1295