The Mississippi River alluvial aquifer is the largest source of fresh ground water in northeastern Louisiana. In 1990, an average of 170 million gallons per day was withdrawn from the aquifer in 12 northeast Louisiana parishes. Additional knowledge about ground-water flow and the effects of withdrawals on the Mississippi River alluvial aquifer is needed for future ground-water development and protection of the resource. Generalized contours of the altitude of water levels in September 1990 and changes of water levels from 1974 to 1990 in the Mississippi River alluvial aquifer in northeastern Louisiana are shown on maps. Water-level trands in the aquifer are shown in hydrographs of selected wells.