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.. There is no doubt that maintaining minimum flows will be one of the major water problems over the next few years and that this problem will probably continue to get worse before it gets. better. For example, the Water Resources Council IS Second National Assessment of the Nation's Water Resources, which is scheduled to go to the printer the first of next month, has attempted to make some rather crude estimates of instream flow requirements for the major river basins and sub-basins in the United States. In the course of this analysis, it was assumed that 60 percent of the average annual flow of a stream would provide a base flow which in turn would provide excellent to outstanding habitat for most aquati c 1 ife forms during thei r primary peri ods of growth and for the majority of recreation uses. It was further assumed that 30 percent of average annual flow would provide good survival habitat for most aquatic life forms. Finally, it was assumed that 10 percent of average flow could sustain only short term survival habitat for most aquatic life forms. This somewhat crude and general analysis indicates that nationally, ideal flow levels for preservi.ng instream uses would total about 1,040 billion gallons per day. With an average daily flow of 1,242 billion gallons per day in 1975 for all river basins in the United States, it appears that flows are adequate at present for fish and wildlife. However, several regions do not reflect such favorable conditions. > For example, the Lower Colorado River has an average daily flow of about 1,550 million gallons per day, while the flow for ideal fish habitat should be almost 6,900 million gallons per day. Needless to say, these national .. and regional estimates are not very useful for purposes of planning water .. resources development and the preservation of minimum streamflows for specific streams. However, they do provide some indication of the national picture. 5