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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5180

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Introduction

Degradation of the aquatic environment by agricultural activities is a major national concern (U.S. Environmental Protection Agency, 2002a). Pesticides are commonly detected in agricultural runoff and in waterways receiving that runoff (U.S. Geological Survey, 1999). Pesticides washed into the waterways can affect nontarget species—killing or inhibiting the growth of beneficial aquatic vegetation and insects, both of which are important to fish communities. Low concentrations of some pesticides interfere with fishes’ ability to detect and avoid predators and with their homing capabilities (Arunachalam and Palanichamy, 1982; Sholtz and others, 2000), and have been implicated in the feminization of frogs (Hayes and others, 2002). Some pesticides accumulate in the tissues of aquatic invertebrates and fish and can pose a risk to people who consume them (Extension Toxicology Network, 1996; Rinella and others, 1993).

Several recent investigations of the occurrence and distribution of pesticides in the Yakima River Basin have been reported by the U.S. Geological Survey (USGS) and by the Washington Department of Ecology. The first basinwide assessment of pesticides was done by Johnson and others (1986) who reported on the occurrence of organochlorine pesticides in water, sediment, and fish from the Yakima River and its major tributaries. Rinella and others (1999) reported on the occurrence of pesticides in water, bed sediment, and biota at about 100 sites throughout the basin. Water-quality samples generally were collected from the Yakima River or from the mouths of tributaries. The occurrence of many current-use pesticides was reported in the study; however, most of the discussion is devoted to explaining the distribution and transport of historically used organochlorine pesticides.

Ebbert and Embrey (2002) reported the occurrence and distribution of historically and currently used pesticides and pesticide degradates from 34 sites on the Yakima River and mouths of tributaries. In addition to documenting the basinwide distribution of pesticides, Ebbert and Embrey documented the temporal variation of pesticide concentrations at three sites during the growing season.

This report builds on the work of these previous investigations, but differs in two significant ways. First, the focus of this report exclusively is on current-use pesticides, and second, most data were collected from small streams and drains rather than the Yakima River or major tributaries. Data for the study were collected as part of the USGS National Water-Quality Assessment (NAWQA) Program. The NAWQA Program monitors and periodically reports on national and regional trends in the quality of water and processes affecting the water-quality (for example, see U.S. Geological Survey, 1999; Gilliom and others, 2006). National and regional reports can be accessed at http://water.usgs.gov/nawqa.

Study Area

The Yakima River Basin is in south-central Washington State. The 15,940 km² basin lies in the rain shadow of the Cascade Range. Mean annual precipitation in the basin ranges from 350 cm in the mountains to less than 25 cm in the eastern lowlands. The western part of the basin is predominantly forested, whereas the eastern uplands are dominated by sagebrush and grasses. The lowlands in the central and eastern parts of the basin support the agricultural communities. The livelihood for many of the basin’s 293,700 residents is based in some way on agriculture. Because arid conditions are prevalent in most of the river basin, irrigation is necessary for farming. During the growing season, a system of storage reservoirs and irrigation canals delivers water to about 450,000 ha of cultivated land. Water deliveries begin in mid-March and cease in mid-October. Further information on the geography, climate, and hydrology of the Yakima River Basin can be found in Rinella and others (1992; 1999).

Purpose and Scope

This report explains the observed distribution of agricultural pesticides at 57 streams, drains, and canals in the Yakima River Basin using information on chemical use, agricultural practices, chemical properties, and physical features of the catchments draining to the sampling sites. The sampled catchments are located throughout the Yakima River Basin, including Kittitas, Yakima, and Benton Counties (pl. 1). The sites were sampled two times during the calendar year 2000.

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