In many parts of the United States, water utilities with highly organic source waters and long source water transmission lines are troubled by Corbicula fluminea, the Asiatic clam. The traditional method of control, free chlorination, often can no longer be used because of the formation of excessive amounts of trihalomethanes (THMs). This study compared the effectiveness of six biocides for controlling the juvenile Asiatic clam. Of the six, monochloramine was found to be the best for controlling the juvenile clams without forming THMs. Includes 50 references, tables, figures.