The use of potassium permanganate for the control of zebra mussels in the Central Lake County Joint Action Water Agency's raw water supply system has been considered a success. Undesirable accumulations of mussels have been avoided while minimizing trihalomethane concentrations in the finished water. Further investigation into the stratification phenomenon observed in the pump station wet well, and system modifications to mitigate the condition will be initiated before next spring's reproductive season. During the first eighteen months of operation, the Agency's staff has developed a better understanding of the requirements of a monitoring system for proper control of the chemical feed system. Several improvements and additional features will be added to the monitoring program for 1994. A more uniform veliger sampling schedule will be used to assure that peak veliger events are identified. A study to compare chemical dose to veliger activity will be performed to improve the dosage selection process. More of the operations staff will be trained in the sampling protocol and mussel identification. Since a few mussels were detected in the ozone chamber, while the samplers at the plant did not register any specimens, the use of a bio box may be considered to improve the monitoring process at the water plant.