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Water Quality Improvement Projects (TMDLs)

Water resource inventory area (WRIA) 34, Washington State.

Water Quality Improvement Projects
Palouse Watershed Area


The headwaters of the Palouse River originate in the forested mountains of Idaho at an elevation of 5,300 ft. It flows for over 165 miles through dryland farming in the central part of the basin and barren rangeland to the west, before its confluence with the Snake River at an elevation of about 500 ft. Major tributaries to the Palouse are the South Fork Palouse River and the Paradise, Rebel Flat, Rock, Union Flat, and Cow creeks.

The Palouse River drains approximately 3,300 square miles of the Columbia Plateau in southeastern Washington and the Idaho Panhandle (see map). Eighty-three percent of the basin is in Washington State, primarily Whitman County. The segment of the river between the Washington-Idaho state line and the town of Colfax is locally referred to as the North Fork. The North and South forks merge at Colfax to form the lower mainstem of the Palouse River. The North Fork contributes about 83 percent of the annual mean flow of the Palouse River at Colfax.

The primary land use is dryland agriculture (67%), with some rangeland (26%) and forested areas (6%) (Sandison et al., 2003). Wheat, barley, lentils, and peas are the major crops. Irrigated farming along the Palouse River and its tributaries contributes less than 1 percent of land use (Wagner and Roberts, 1998). With a population of only about 47,000, urban areas make up less than 1 percent of the basin in Washington.

Water quality issues

Several streams in the Palouse River watershed currently do not meet Washington State’s water quality standards for several parameters. Parameters of concern include dissolved oxygen; fecal coliform bacteria; pH; temperature; and toxics.

Why this matters

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

To learn more about the importance of these various parameters, please see our water quality impairments page.

What is being done

To address these water quality issues the Department of Ecology (Ecology) is establishing water quality improvement projects (also know as a Total Maximum Daily Load or TMDL) in several areas in the watershed. A water quality improvement project is a public process in which local organizations and citizens develop actions designed to reduce pollution and bring a water body back to a healthy condition. They are established for each water quality problem to protect all designated “beneficial uses” of the river, including swimming, boating, fishing, providing aquatic habitat, providing aesthetic value, and supplying drinking, irrigation, and industrial water.

Project information

Related Information

Overview of the Total Maximum Daily Load (TMDL) process (PDF)

Environmental Protection Agency (EPA)

Transforming Watersheds: Palouse River - Whitman County (Ecology water quality story)

Direct Seeding: The Environmental Magic Bullet (Ecology water quality story)


Contact us for more information

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Last updated April 2015