Water Quality Improvement Project
Tucannon Watershed Area:


The Tucannon/Pataha watershed is located in southeastern Washington State in Garfield and Columbia counties. The Tucannon River drains a watershed area of approximately 318 square miles. It flows into the Snake River 4 miles upstream of Lyons Ferry state Park. Pataha Creek enters the Tucannon River about 11 miles above the Tucannon’s confluence with the Snake River. The Pataha drains a watershed of 185 square miles.

The Tucannon basin ranges from 540 feet (165 meters) above sea level at the confluence of the Tucannon and the Snake River, to 6,400 feet (1,950 meters) above sea level in the Blue Mountains. The climate is semi-arid. Average annual precipitation ranges from 5-10 inches in the lowlands of the Snake River up to 45 inches in the Blue Mountains.

Historically the lower elevation areas were covered with canyon grasslands and shrub-steppe vegetation. Much of this land has now been converted to livestock and crop (mainly non-irrigated crops such as wheat) production. Coniferous forests still dominate the higher elevations of the Blue Mountains. Much of this area is under state or federal ownership. Land use in the watershed is primarily rural with few urban areas. The city of Pomeroy is the most populated area in the watershed, with a population in the year 2000 of 1,517.

Water quality issues

Water quality standards are designed to protect the beneficial uses of our streams and lakes. Beneficial uses can include drinking water, irrigation, fishing, habitat and recreation (swimming, wading, and boating). When a water body does not meet Washington State water quality standards it is placed on the state’s Section 303(d) list of impaired water bodies.

The primary water quality concerns in the Tucannon River and Pataha Creek are temperature, fecal coliform and pH. Both waterbodies were placed on the 303(d) list for exceeding state water quality standards for these parameters. The Tucannon River was also listed for turbidity. To learn more about these parameters please visit The Environmental Importance of the Different Impairments page.

Once placed on the 303(d) list, a water quality improvement project (also known as a Total Maximum Daily Load, or TMDL) is normally completed. Visit the TMDL web site for more information on TMDLs. Information about Ecology’s 303(d) listings is available by visiting the Water Quality Assessment web site.

Why this matters

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. Threatened and endangered salmon need cold, clean water to survive.

One way to cool water temperature is to shade the water body by adding or retaining streamside vegetation.

Tucannon River, Washington State. Photographer unknown.

What is being done

Temperature problems in the Tucannon and Pataha creeks are being addressed through a streamlined Total Maximum Daily Load (TMDL) approach.

The streamlined approach is simpler and faster than the conventional TMDL method. It works by:

  • Using as much existing local data and data collection resources as possible.
  • Avoiding complicated computer modeling when feasible.
  • Writing TMDL reports that are as short and clear as possible.
  • Writing reports that are more management-focused.
  • Getting water quality improvements on the ground as soon as possible, supporting existing efforts.

This particular TMDL project was selected for an innovative approach because:

  • The water quality problems are mainly from non-point sources. This makes it easier to determine what the problems are and how to fix them.
  • The Snake River watershed, where the Tucannon/Pataha watershed is relatively small. Small watersheds tend to have less complicated water quality problems, and so are easier to fix.
  • Some data needed to do a TMDL in this watershed already exists. This reduces the amount of sampling work Ecology needs to do.
  • Local governments and citizens are already implementing some actions to address water temperatures, so the creeks are already on the fast track to recovery.

The streamlined TMDL process is being piloted in the Tucannon/Pataha watershed by addressing temperature first. We chose temperature because of all the parameters that are identified as problems in the watershed, temperature is perhaps the best fit for this type of process. Once this TMDL is complete the intention is to apply the lessons learned to address the remaining parameters using similar streamlined TMDL procedures.

Status of the project

Ecology’s staff developed a technical analysis of the temperature problem in the watershed. They refined the report, assisted by the WRIA 35 watershed planning unit, which agreed to serve as the advisory group for the TMDL. They completed a draft report showing the results and recommending remedial actions.

The draft report was reviewed by the public during a comment period ending May 21, 2010. Ecology addressed comments received and submitted the final version of the TMDL-implementation plan (water quality improvement report, or WQIR) to EPA for approval on July 14, 2010. EPA approved the WQIR on September 27, 2010.

Technical information

There are a number of possible factors that could cause a water-body’s temperature to rise, altered hydrologic function and lack of riparian shade being perhaps the most significant. Of these, riparian shade is the easiest problem to address, and is therefore usually the focus of implementation work.

The streamlined TMDL approach, piloted in the Tucannon/Pataha watershed, uses a shade deficit method to calculate a shade target for the Tucannon and Pataha Rivers and their tributaries. Simply put, this approach uses GIS and high-resolution aerial photographs in conjunction with a computer model to determine a shade target by calculating the system potential shade and subtracting existing shade. Shade information will be combined with hydrologic data to prioritize reaches for restoration. The person managing implementation is responsible for applying the shade estimates to determine what kind of riparian restoration is required for a particular reach they’re working in.

This technical work replies heavily on previous field data collected by various organizations in the watershed. Ecology did not collect any new field data for this project. The exception is the temperature data collected at the only two point source discharges – the Pomeroy wastewater treatment plant and the Tucannon fish hatchery. These data are included in the shade work used to develop a TMDL that addresses all temperature problems across the entire watershed.

Tucannon River and Pataha Creek Temperature TMDL - Water Quality Improvement Report and Implementation Plan (Ecology publication)

Related information

WRIA 35: Watershed Planning (Asotin County)
http://www.asotinpud.org/watershedplanning/index.html (not available online)

Snake River Salmon Recovery Board

Transforming Watersheds: Middle Tucannon River - Columbia County (Ecology Water Quality story)

Pomeroy Wastewater Treatment Plant: Effluent Dissolved Oxygen Solution (Ecology Water Quality story)

WRIA 35: Middle Snake Watershed Information (Water website)


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Last updated August 2016


WRIA: #35 (Middle Snake)
County: Garfield

Water-body Names:
Tucannon River
Pataha Creek


# of TMDLs: 22

Streamlined TMDL project
TMDL 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