The Lower Missouri Basin encompasses that region drained by the Missouri River and minor tributaries between the Niobrara and the Mississippi Rivers. The area is about 640 miles in length, 140 miles in maximum width, and 40,970 square miles in area, including parts of the States of Iowa, Kansas, Minnesota, Missouri, Nebraska, and South Dakota. The region considered in this report generally has sufficient water for most uses, and frequently has too much water. The land and water resources conservation program will retain flood flows for beneficial use and, with ultimate development, will control and increase discharge in the Missouri River during periods of low flow. A study of sources of pollution and their effects on the main stem of the Missouri River as detected by physical, chemical, biochemical and bacteriological tests is reported.