A river management system for controllably operating devices of management facilities installed at pluralities of rivers and waterways to manage water volumes in a river network including the pluralities of rivers and waterways. The river management system includes an operation plan database for storing therein a plurality of sets of the contents of operations of the river management facility devices in the form of operation modes when the values of water levels, flow rates, precipitations and change rates thereof at a plurality of points of the river network satisfy predetermined conditions; an operation plan decider, when the values of water levels, flow rates, precipitations and change rates thereof at the points of the river network satisfy the predetermined conditions, for selecting one of the operation modes corresponding to the conditions and determining the operation contents of the river management facility devices; and a monitor/input section for inputting values of water levels, flow rates and precipitations of the points of the river network to the system.