Yakima River Water-Quality Studies

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 were conducted in 59 areas throughout the Nation to provide a framework for national and regional water-quality assessment. Together, these areas accounted for 60 to 70 percent of the Nation's water use and population served by public water supplies, and covered 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 greatly increased concentrations of suspended sediment, nutrients, trace metals, pesticides, and fecal-indicator bacteria in streams that received irrigation-return flows. Additionally, more than 50 pesticides and breakdown products were identified in water, sediment, and fish in the lower basin.

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