A case study was made to determine least-cost systems for achieving specific water quality levels of the Wisconsin River Basin (Wisconsin). To initiate least-cost systems, institutional prerequisites were analyzed and alternative institutional structures considered. By application of a predictive water quality model based on dissolved oxygen and analysis of costs influencing DO levels, costs of systems to meet specified objectives are determined indicating that substantial economics can be realized by utilization of a regional management system. Alternative policies and organizational arrangements are assessed. Potential and equitable economies could be realized with substantial changes in policy framework; an effluent-charge system would prove unnecessarily costly and its administration difficult; effective results can be achieved by a combination of regulation and cost sharing of system management by waste producers. Criteria of organizational design are established and applied to three alternative organizational arrangements. An organizational system including a quasi-judicial body (to establish standards), a state water resources agency (to monitor environmental interests), and a regional implementing and operating agency would most effectively meet the desired criteria. (WRSIC abstract)