It is the custom for paper mills located alongside the Layzee River to discharge waste products into the river. As a result, operators of hydroelectric power-generating plants downstream along the river find that they must clean up the river's water before it flows through their equipment. Based on the preceding information, which of the following policies would be most appropriate for dealing with this problem?

a. The demand for the output from the hydroelectric power plants to decrease
b. The supply of the output from the hydroelectric power plants to decrease
c. The demand for the output from the hydroelectric power plants to increase
d. The supply of the output from the hydroelectric power plants to increase