Salinity is the most serious water quality problem in the Colorado River Basin. The impact, felt largely in the Lower Basin, is acute because the basin is approaching conditions of full development and utilization of all available water resources. Current estimates indicate that each mg/1 increase in concentration at Imperial Dam results in $450,000 annual damages. Therefore, in order to offset salinity caused by the development of the vast energy supplies and to allow the seven Colorado River Basin states to fully utilize their allocation of Colorado River water, it is necessary to implement cost-effective salinity control programs in the basin. A simple multi-level nonlinear optimization procedure was utilized to formulate the most cost-effective array of salinity control strategies for the Upper Colorado River Basin. The incremental cost-effectiveness methodology qualitatively indicates the location and general type of alternatives to be implemented in a least cost basin-wide salinity control program. The results also qualitatively indicated the anticipated salt load reduction and expected annual costs of each salinity reduction increase for any preselected level of control. The analysis was limited to projects designated in PL 93-320. Costs and salinity contributions associated with various alternatives were generated using January, 1980, estimated conditions. Cost-effectiveness functions were developed for each of the major canals and laterals, the aggregate laterals under each canal, and an array of on-farm improvements for each agricultural project area. Similar functions were also developed for point sources such as Paradox Valley, Glenwood-Dotsero Springs and Crystal Geyser. Collection and desalination of agricultural return flows were also considered. Marginal cost analysis based on current damage estimates indicate that the optimal cost-effective salinity control program in the Upper Basin would cost about $30 million annually and remove about 1.2 million megagrams of salt per year. In addition, it was concluded that maintenance of the 1972 salinity levels at Imperial Dam cannot be cost-effectively achieved and should be allowed to rise by as much as 180 mg/1. Optimal salinity control programs are presented for the individual alternatives, for individual areas or projects, for the states of Colorado and Utah and the Upper Colorado River Basin. Sensitivity analysis showed that very large errors in costs and component salt loading would have to be evident to change the optimal salinity control strategy for the Upper Colorado River Basin.