In 1998 and 1999, the U.S. Geological Survey (USGS) completed comprehensive studies of nitrate concentrations in ground water in the Henrys Fork Basin in eastern Idaho (fig. 1A). These studies were done in cooperation with the following agencies or groups: Idaho Division of Environmental Quality (DEQ), District 7 Health Department, Idaho Department of Water Resources (IDWR), Idaho Department of Agriculture (IDAG), Bureau of Reclamation, Henrys Fork Foundation, Fremont County, and Madison County. This Fact Sheet presents selected results of these investigations.