In 1981 the state of Wisconsin initiated a trading program for the point source dischargers-primarily paper mills and sewage treatment plants-along the Fox River. The state initiated the program in an effort to meet water quality standards for biological oxygen-demand pollutants. Under the program, the state (1) established a total waste load goal; (2) imposed more stringent limits on individual dischargers; and (3) under limited conditions, allowed the dischargers.