USGS
Water Resources of Idaho

National Water-Quality Assessment (NAWQA) Program
Upper Snake River Basin Study

INTRODUCTION

The 35,800 square-mile upper Snake River Basin is located in southeastern Idaho and northwestern Wyoming and includes small parts of Nevada and Utah (Basemap figure). Total population in the basin was about 425,000 in 1990. Major urban areas are Idaho Falls, Pocatello, Rexburg, and Twin Falls. Climate in the basin is mostly semiarid and mean annual precipitation ranges from 8 to more than 60 inches (Precipitation figure).

The Snake River flows about 453 miles from the southern border of Yellowstone National Park in Wyoming to King Hill, Idaho. There are five reservoirs on the Snake River that provide a total storage capacity of more than 4 million acre-feet. The Snake River Plain aquifer underlies the eastern Snake River Plain and stores between 200 to 300 million acre-feet of water predominantly used for irrigated agriculture. Major crops in the basin include potatoes, wheat, sugar beets, hay and barley. About 21 percent of the basin is agricultural land and 50 percent is rangeland.

Water Quality and Biological Issues

Nonpoint-source activities that affect surface water are irrigated and nonirrigated agriculture, rangeland grazing, land and road development, streamflow regulation from dams and diversions, and recreation. Activities within the basin that create potential point-source contaminants include industrial or municipal wastewater treatment facility, aquaculture and animal feedlot effluents. Increased concentrations of sediment, bacteria, nutrients, and pesticides as well as organic enrichment and increased water temperatures in selected reaches of the Snake River are water-quality issues of concern.

Potential for ground-water contamination from point and nonpoint sources are associated with agricultural activities and focus on elevated pesticide and nutrient levels. Other potential point sources of contamination are from confined animal operations, feedlots, petroleum storage tanks, industrial chemical leaks and spills, and application of wastewater to the land.

Biological impacts within the study unit are derived from activities such as stream alterations, water resource development, irrigated agriculture, aquaculture, grazing and foreign species introduction. The loss of cold water habitat and aquatic life in the Snake River between Milner Dam and King Hill are of special concern and are the focus of many agency activities.

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