Water Quality in the Yakima River Basin

In 1991 the U.S. Geological Survey initiated the National Water-Quality Assessment (NAWQA) Program to assess the status and trends in the quality of freshwater streams and aquifers, and to provide a sound understanding of the natural and human factors that affect the quality of these resources. As part of the program, investigations will be conducted in 59 areas--called study units (click opens new window)--throughout the Nation to provide a framework for national and regional water-quality assessment. Together, these areas account for 60 to 70 percent of the Nation's water use and population served by public water supplies, and cover about one-half of the land area of the Nation.

Prior to the implementation of the full-scale NAWQA program, in 1986, the USGS implemented a pilot program to test and refine the concepts for the nationwide program. The Yakima River Basin in south-central Washington was selected for one of four surface-water pilot studies. The Yakima Basin pilot program showed that agricultural practices in the basin can greatly increase concentrations of suspended sediment, nutrients, trace metals, pesticides, and fecal-indicator bacteria in streams that receive irrigation-return flows. Additionally, more than 50 pesticides and breakdown products were identified in water, sediment, and fish in the lower basin.

During the current cycle of the Yakima River Basin NAWQA study, which will extend from 1999 through 2002, USGS scientists will analyze surface water for pesticides, nutrients, trace elements, fecal-indicator bacteria, and ecological health, as measured by biological diversity. The data gathered will enable scientists to assess the health of the aquatic system and to examine the processes affecting water quality in the basin. The information gained during this study will help enable irrigators, water managers, regulators, and the public make informed decisions about the use of the surface-water resource of the Yakima River Basin.