Lower Yakima watershed pesticides reduction project

Water quality testing found pesticide residues in the Yakima River and some of its tributaries. Most of these chemicals are banned pesticides that are no longer used, called persistent legacy pesticides. The Yakima River originates on the east side of the Cascade Mountains near Snoqualmie Pass. The confluence of the Yakima River and Naches River at the city of Yakima divides the Yakima River into upper and lower portions. We are working with local organizations and residents to cleanup the lower Yakima River.

Water quality issues

The lower Yakima River basin is an intensively farmed and irrigated area. Past studies show that legacy pesticides, such as DDT, get into the water when polluted soil erodes and enters the water. Some of these compounds were also found in fish in the lower Yakima River and some of its tributaries. 

We completed a study of water quality conditions in the Yakima River watershed in 2010. The study found that nonpoint sources of pesticides continue to be the main cause of contamination in the river and tributaries. The study also determined that changes in agricultural practices have greatly reduced the amount of pollution coming from irrigation runoff. A 2016 study of Yakima River fish found that, while contamination levels in these fish have declined over the years, some fish still do not meet standards in the lower Yakima River.

What we have done

Farmers and other land users in the lower Yakima River watershed implemented the Lower Yakima Sediment total maximum daily load (TMDL) plan. Their dedicated work has significantly reduced some of the water quality problems in the watershed. The Roza Sunnyside Board of Joint Control adopted water quality policies that reduce the amount of polluted runoff entering tributaries of the Yakima River. Many agricultural operations adopted practices that prevent or reduce their impact to streams.

In 2016, we convened a stakeholder work group to help decide on the best and quickest path to clean up the river. Since most of the pollution is still in the lower Yakima Valley, the work group's initial focus is on reducing nonpoint sources of pesticides in the lower Yakima Valley. We will continue our efforts with the work group, and with lower valley community groups to reach water quality goals in the watershed.

Status of the project

Based on the findings and recommendations in the 2010 technical study, we're developing a new water quality improvement project called the Lower Yakima Watershed Pesticide Reduction Plan. This project includes an evaluation of current levels of legacy pesticides and chlorpyrifos in the lower Yakima River valley, sets human health cleanup targets for these pesticides, and lays a path to achieve these targets. 

We will continue to monitor sediments and turbidity — as well as pesticides being addressed by this project — to measure the progress of other water quality improvement project actions. These efforts will help bring the watershed into compliance with state water quality standards.


Our Lower Yakima Watershed Pesticide Reduction Plan will outline specific recommendations for nonpoint sources of pesticides. For growers, improvements in irrigation practices and water management may be necessary to address the high percentage of pollution that still comes from erosion from farms. Pesticides adhere to soil, so it will be important to reduce soil eroding into major drains and tributaries to the Lower Yakima to meet water quality targets.

Why this matters

Legacy pesticides, which are persistent chemicals in the environment, are a growing concern for the state. In the lower Yakima River valley, these chemicals are mostly from agricultural pesticides. They can contaminate the food (fish, shellfish, etc.) and can be found in water, soil, wildlife and even in people's bodies, which may lead to health problems.