This is the Ninth in a series of annual reports covering the activities of the Water Resources Research Center, University of Minnesota. The report indicates the nature of the program conducted in the twelve months beginning July 1, 1972, and ending June 30, 1973, with funds provided by the Graduate School and the Office of Water Resources Research in connection with the Water Resources Research Act of 1964. The Center supported 18 research projects involving 19 faculty members. These research projects were concerned with: mathematical watershed system analysis, aquatic plants, eutrophic lakes, groundwater basin information, water resources research planning, soil water movement, Mississippi river ecology, perception of water resources problems, financing of water resources development, water pollution and social factors, forest management, water resources policies, sub-surface irrigation, flood forecasting, water policy decisions, precipitation variations, and floods.