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monthly flows at the 1970 level of development were computed, as for Hermann. Table 3 shows the average percent contribution from the eight subbasins to the average annual flow of the Missouri River under 1970 conditions. The eight subbasins contribute 55.5 million acre-feet of flow which is subject to an additional 1.9 million acre-feet of main stem reservoir evaporation and other depletions, leaving a net basin outflow of 53.6 million acre-feet. Table 3 - SUBBASIN FLOW CONTRIBUTIONS TO THE MISSOURI RIVER Drainage Area I970-LeveI Flow Thousand Percen t MiUion Percent Subbasin Sq. Mi. of Basin Ac. Ft. of Basin Upper Missouri 92 17 7.7 14 Yellowstone 71 13 8.8 16 Western Dakota 77 15 2.4 4 Eastern Dakota 58 11 3.2 6 Platte-N iobrara 99 19 4.2 8 Middle Missouri 25 5 7.7 14 Kansas 61 12 4.2 8 Lower Missouri 40 8 17.3 30 Subtotals 523 100 55.5 100 Main Stem Depletions -1.9 - Missouri Basin (Hermann, Mo.) 523 100 53.6 100 Surface-Water Quality Pure water in streams and lakes is practically unavail- able. Water is a solvent and it dissolves and carries in solution certain materials derived from the soils and rocks over which it flows or through which it percolates. In addition to the natural sources of dissolved solids, human activity in many endeavors either directly or indirectly contributes dissolved solids to streams. Streams also may transport many undissolved solid wastes accumulated from natural overland runoff, or deliberately discharged to the streams as wastes. The following paragraphs highlight the present quality of surface wafers, while more uelail may be round in the appendix, "Hydrologic Analyses and Projections." Water quality is judged largely in terms of the requirements of the various water uses. Within the Missouri Basin, the primary water uses are domestic, industrial (including power generation and cooling water), irrigation, recreation, fish and wildlife, and navigation. Water quality demands vary for each use, and also may vary within a region for a given type of use. The principal water quality characteristics that concern the suitability of water for uses within the basin are the dissolved solids content that affect the health of humans and plant and animal life; temperatures that affect the fishery and aquatic environment; pathogens that affect health; and taste, odor, and floating materials that may affect adversely the potability of the water and the general environment. Bacterial and biological pollutants in the form of micro-organisms may not only endanger health, but also may reduce the dissolved oxygen content of streams and lakes and make them less desirable as fishery habitat. Temperature is a quality that is often complex in its effect upon the biological regime 18 and fishery habitat. Undissolved solids such as sludges, floating material, oils, and sediments are visible and, when observed, often generate a demand from the public for remedial measures. Quality standards for the various uses of water in the Missouri Basin are discussed in the appendix "Present and Future Needs." The amount and kinds of water quality data obtained within the basin largely have been responsive ro problems encountered in the use of water. Historically, and aside from bacterial and biological aspects, the principal concern has been the concentration of those dissolved solids that affect domestic, industrial, and irrigation uses. Figure II shows the total dissolved solids concentratIon in miiiigrams per liter for general areas as derived from 77 stream-sampling stations. Similar addi- tional data were derived for critical parameters such as sulfates, chlorides, and sodium adsorption ratios. Temperature data have been obtained at several stream-sampling stations within the basin and, in general, average water temperatures are approximately the same as the average daily air temperatures, except as affected locally by thermal pollution. There has been no systematic program for obtaining biologic data or dissolved oxygen data on an area-wide basis. The data that are available have been obtained in association with problem areas as discussed in the appendices "Hydrologic Analyses and Projections" and "Present and Future Needs." Sediment From the standpoint of erosion characteristics and sediment contributed to streamflow, the Missouri Basin is a diverse area, and to develop simple formulae for a determination of sediment yields within the basin is impossible.