An evaluation is presented of the influence of water quality standards on the planning and development of a river basin and on the treatment requirements for wastewater discharges. The Big Sioux River in eastern South Dakota was selected for a case study because the river was largely uncontrolled although intensive investigation was underway for water resources development including multiple purpose reservoirs. Existing flow and water quality data for the river were evaluated and the influence of increased water requirements for irrigation and domestic use was projected to the year 2010. For extended periods of time, the river flow has been exceeded by wastewater discharges. Multiple linear regression was used to develop a mathematical expression for the minimum dissolved oxygen in the river in terms of flow, temperature and BOD for both summer and winter conditions to predict future river flow requirements from proposed reservoirs to maintain the assigned water quality for the proposed beneficial uses. Although a city with a population equivalent of 450,000 persons presently provides 96 to 98% BOD removal, additional treatment of wastewater is required to meet the imposed water quality standards. (WRSIC abstract)