The study described in this report, initiated by the U.S. Geological Survey in 2006, was designed to evaluate available fresh groundwater reserves within the Mississippi embayment, South-Central United States, as an area within a broader national assessment. The goals of the national assessment are to document effects of human activities on water levels and groundwater storage, explore climate variability effects on the regional water budget, and evaluate the adequacy of data networks at a regional scale. The Mississippi embayment was chosen as a study area in the national assessment because of the substantial dependency on groundwater for agriculture and municipal needs.