Water Quality Improvement Project
Pataha Creek Area:


Pataha Creek is located in Pataha, Washington, which is a small town in Garfield county, southeastern Washington State. The creek is along the Nez Perce trail, which was a path used by the original Nez Perce Native Americans to cross the Rocky Mountains.

The Pataha Creek watershed covers Garfield and Columbia counties. Tributaries to the creek include Dry Pataha Creek, Sweeney Gulch, Balmaier Gulch, Tatman Gulch, and Dry Hollow (HDR, 2005). Land use in the area includes agriculture (irrigated and non-irrigated) and forest for timber harvest in the upstream sections of the creek.

Water quality issues

In 1992, a limited Class II Inspection and Receiving Water Study on Pataha Creek determined that because Pataha Creek is small it may have some difficulty in effectively diluting the effluent discharged from the Pomeroy wastewater treatment plant (WTP). The study found that the creek received high nutrient loads from the WTP, as well as elevated nutrient concentrations upstream of the WTP, possibly from urban and agricultural activity. Survey data showed violations for fecal coliform concentrations, chronic ammonia, and dissolved oxygen. The creek was also found to have a reduced ability to assimilate the biological oxygen demand (BOD) load during the summer because of elevated water temperatures resulting in low dissolved oxygen.

A 1997 ambient monitoring study reported that Pataha Creek exhibited high temperature, pH, and fecal coliform bacteria issues.

Pataha Creek, Washington State.  Photo courtesy of Martin Schrattenholzer via Flickr.
© Martin Schrattenholzer.

Why this matters

Ammonia (NH4+) is one measure of nitrogen, a nutrient that can increase the growth of plants and algae in water. When higher-than-normal levels of nutrients are present, plants and algae can get out of control and lead to changes in the water’s pH, dissolved oxygen 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.

Chlorine is a gaseous halogen (nonmetal element) used mainly to purify water, as a disinfectant and bleaching agent, and to make compounds like plastics, solvents, textiles, agrochemicals and pharmaceuticals, insecticides, household cleaning products, etc. Because it is one of the more reactive group of elements, it combines readily with nearly all elements. This makes it a strong oxidizer.

Chlorine is a toxic gas that irritates the respiratory system, due to its oxidizing abilities. Its oxidizing abilities may also cause it to react with flammable materials.

Status of the project

Ecology submitted a TMDL containing three wasteload allocations (WLAs) to Pomeroy WTP, and three load allocations (LA) for a segment of the Pataha River. EPA approved the TMDL submittal on September 9, 1994. The WLAs were incorporated into Pomeroy's WTP permit upon renewal in 1993. The LAs were expected to be maintained through voluntary compliance.

Technical information

Pataha for Ammonia-N, BOD, and Chlorine TMDL (Ecology publication)

Related information

WRIA 35: Middle Snake Watershed Information (Environmental Assessment Program web site)

River and Stream Ambient Monitoring Report for Water Year 1997 (Ecology publication)

HDR Memo to WRIA 35 Planning Committee, Asotin PUD, March 10, 2005
www.asotinpud.org/msww/documents/Pataha_Creek_FC.pdf (not available online)

WRIA 35: Middle Snake Watershed Information (Water website)

Back to top of page

Last updated August 2016
  Watershed map for water resource inventory area (WRIA) 35, Washington State.


WRIA: #35 (Middle Snake)
County: Garfield

Water-body Name:
Pataha Creek

Biochemical Oxygen Demand (BOD)

# of TMDLs: 3

Approved by EPA

Contact Info:
David T. Knight
Phone: 509-329-3590
Email: David.T.Knight@ecy.wa.gov

Eastern Region
Department of Ecology
N 4601 Monroe
Spokane, WA 99205 -1295