Water Quality Improvement Project
Palouse River Area:
Dissolved Oxygen & pH


As part of a larger effort to address all water quality impairments in the Palouse River watershed, Ecology began a project to address low dissolved oxygen and high pH in Palouse River in 2007. This project only addresses the portion of river known locally as the North Fork Palouse River (from the state line with Idaho to the confluence with the South Fork Palouse River in Colfax). The mouths of major tributaries through this section of river are also included.

Dissolved oxygen and pH impairments along the rest of the Palouse River will be addressed in the future. Dissolved oxygen and pH impairments in the South Fork Palouse River watershed are being addressed as a separate project. Please see the South Fork Palouse River Project page for more information on studies in this sub-watershed.

Why this matters

The levels of dissolved oxygen and the pH of the water are vital to the health of the fish, animals, and insects that live there. When a river is outside of healthy conditions fishery populations decline, which diminishes the resource for recreational and subsistence fishing. Additionally, the pollutant that causes low dissolved oxygen levels and wide pH swings in the North Fork Palouse River is nitrogen, a nutrient that supports plant growth. When this nutrient is in excess, algae and other plants grow at elevated rates in the water, leading to unsightly algal blooms and surface scum. These conditions lessen the aesthetic value of the river. The summer of 2014 saw both significant algal blooms and fish kills, which may in part be attributed to these impairments.

Status of the project

Data for this study was collected in conjunction with the bacteria study in 2007, and intensive surveys were conducted in the summers of 2007 and 2012. The study found that the periphyton (bottom algae), which drive dissolved oxygen and pH in the North Fork Palouse River, are extremely sensitive to inputs of dissolved inorganic nitrogen (DIN). DIN is the combination of nitrate, nitrite, and ammonia. Background levels of DIN in the river are near zero, and even small DIN inputs can have large impacts on dissolved oxygen and pH. This means that to restore natural dissolved oxygen and pH levels in the watershed, DIN needs to be reduced to near-zero levels during May-October. The primary form of nitrogen in this system is nitrate.

Ecology developed a report detailing the findings of the study, including the amount of pollutant that can be allowed in the river without causing an impairment. This report is required by the Clean Water Act for streams violating water quality standards and is called a total maximum daily load (TMDL).

Ecology worked with several organizations in the watershed to draft an implementation plan describing methods to address issues contributing to elevated nitrogen. Some of these methods include reducing dissolved inorganic nitrogen in wastewater effluent, elimination of effluent from failing septic systems, prevention of soil erosion flowing to waterways, and the reduction of human and livestock impacts to stream corridors and stream banks.

The study findings and implementation plan are combined into a single report outlining how dissolved inorganic nitrogen will be reduced to achieve water quality standards for dissolved oxygen and pH. The TMDL study and implementation plan underwent a public review and comment during the summer of 2015. The report was submitted to the Environmental Protection Agency (EPA) for their review and approval on November 2015. EPA approved it in December 2016.

Technical information

North Fork Palouse River Dissolved Oxygen and pH Total Maximum Daily Load : Water Quality Improvement Report and Implementation Plan

Presentation on the Dissolved Oxygen and pH TMDL Study and Implementation Plan given at the August 3, 2015 Public Meeting in Palouse, WA

Palouse River Dissolved Oxygen and pH Total Maximum Daily Load Study-Water Quality Study Design (Quality Assurance Project Plan)

Addendum 2 to Quality Assurance Project Plan: Palouse River Dissolved Oxygen and pH Total Maximum Daily Load Water Quality Study Design

Related information

WRIA 34: Palouse Watershed Information (Environmental Assessment Program web site)


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Last updated December 2016


WRIA: #34 (Palouse)
County: Whitman

Water-body Names:
North Fork Palouse River

Dissolved Oxygen

# of TMDLs: 28

TMDL approved by EPA, has implementation plan.

Contact Info:
Elaine Snouwaert
Phone: 509-329-3503
Email: Elaine.Snouwaert@ecy.wa.gov

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