The Earl Water Filtration Plant (ESFP) is a conventional treatment plant operated by the Castaic Lake Water Agency (CLWA) in Castaic, California, with two parallel trains of flocculation (alum) and sedimentation basins (with tube settlers) followed by filtration. Chlorine is added at several points in the process train, to achieve disinfection and prevent algae growth. Approximately half of the chlorine is added solely for algae control. The addition of this excess chlorine prevents the reduction of Bio-Degradable Organic Carbon (BDOC) via biologically mediated processes such as biologically active filtration (BAF). BDOC reacts with the chlorine to form Disinfection Byproducts (DBPs), most notably trihalomethanes but also haloacetic acids. However, algae has the effect of clogging the tube settlers, weirs, and filters, it can damage the concrete walls of the basins, and it can cause taste and odor problems. A uniuqe solution to this problem has been to cover the basins with floating covers. Properly designed covers prevent algae growth without the application of chlorine. In the first year of study, one process train was covered with floating covers and the other left open and chlorinated. The TOC, Bio-Degradable Organic Carbon (BDOC), and all DBPs were measured in each train for a six month period. Results show significant reductions in TOC, BDOC, and DBPs. In the second and third years of study both trains were covered and chlorine was removed first from both trains and then from the filters. Significantly reduced concentrations of DBPs were observed not only at the plant effluent but also in the distribution system. Reduced BDOC was not observed. Includes 7 references, figures.