Cropping systems may have an unfavorable influence on the quality of nearby surface water. Linear programming methods were used to assess the impact of improvements in certain water quality characteristics on economically optimal crop systems. Thus, the effect of crop practices on water quality is analyzed indirectly by assuming that farmers would alter their cropping practices in the most economical way in order to conform to various water-quality constraints. A 1,200-acre watershed was used to illustrate the procedure. Sediment entering the reservoir was treated as a variable constraint on maximization of farm income. Requiring successively lower amounts of sediment to enter the reservoir caused farm income to decrease at an increasing rate. (Modified author abstract)