Yakima watershed toxics reduction project

Water quality testing found toxic chemicals in the Yakima River and some of its tributaries. Most of these chemicals are banned pesticides or PCBs (polychlorinated biphenyls) that are no longer used. We are working with local government and citizens to clean up these persistent “legacy” pesticides.

Yakima River overview

The Yakima River originates in Kittitas County, located on the east side of the Cascade Mountains near Snoqualmie Pass. The confluence of the Yakima and Naches Rivers (one of its tributaries) at the city of Yakima divides the Yakima River into "upper" and "lower" portions.

Water quality issues

The lower Yakima River basin is one of the most intensively farmed and irrigated areas in the United States. Past studies show that some legacy pesticides get into the water when contaminated soil erodes and enters the water. Some of these compounds were also found in fish living in the Yakima River and some of its tributaries. 

What we have done

We conducted a study on water quality conditions in the Yakima River watershed in 2006. Although the study found additional sources of toxic water contamination to the surface waters, the study also determined that changes in agricultural practices have reduced the amount of pollution coming from irrigation runoff. While some Yakima River fish still have pesticides in their flesh, the levels are much improved (reduced) compared to previous years. This reduction in pesticide levels in fish tissue allowed the Washington Department of Health to drop its advisory on DDT in most of the lower Yakima River fish species.

Farmers and other land users in the watershed implemented existing total maximum daily loads (TMDLs) that may have helped some of the water quality problems. The Roza Sunnyside Board of Joint Control and Kittitas County Water Purveyors adopted water quality policies that reduce the amount of polluted runoff entering into tributaries of the Yakima River. Many agricultural operations adopted practices that prevent or reduce their impact to streams.

The technical study for the Yakima Watershed Toxics Reduction Project was published in 2010.

In 2016, we convened a stakeholder work group to help decide on the best path to clean up the river most quickly. Since most of the pollution is still in lower Yakima Valley, the initial focus of the work group will be reducing lower Yakima Valley nonpoint toxic pollution sources. This work group will work with lower valley community groups to continue to reach water quality goals in the watershed.

Status of the project

Based on the findings and recommendations in the Yakima Watershed Toxics Reduction Project technical study, we are developing a new water quality improvement project that includes a new evaluation of current levels of DDT in the lower Yakima River valley, sets human health clean-up targets for DDT, and lays a path to achieve these targets.

We will continue to monitor sediments and turbidity as well as legacy pesticides to measure the progress of other water quality improvement project work. These efforts will help bring the watershed into compliance with state water quality standards.


Since a high percentage of the pollution in the lower Yakima watershed still comes from soil erosion from farms, growers who have not made changes in irrigation practices and water management need to do so now. Sediment from farmland, including pesticides that adhere to the sediment particles, must be further reduced in major drains and tributaries to meet targets outlined in the Ecology report. Other sources will be assigned load reduction targets as part of the Yakima Watershed Toxics Reduction Project.

Why this matters

Toxic chemicals, which are persistent chemicals in the environment, are a growing concern for the state. They can contaminate the food (fish, shellfish, etc.) that people might eat. In the Yakima River valley, these chemicals are mostly from agricultural pesticides and industrial pollution. They can be found in air, water, soil, and wildlife. And they are showing up in people's bodies, which may lead to health problems.