Frequent and severe occurrences of harmful algal blooms increasingly threaten human health by the release of microcystins (MCs). Urgent attention is directed toward managing MCs, as evidenced by rising HAB-related do not drink/do not boil advisories due to unsafe MC levels in drinking water. UV/chlorine treatment, in which UV light is applied simultaneously with chlorine, showed early promise for effectively degrading MC-LR to values below the World Health Organization's guideline limits. Still, much is unknown regarding potential disinfection byproduct formation and associated toxicity, which can occur from the reaction of chlorine and other reactive species with MCs and algal and natural organic matter. To ensure UV/chlorine guarding drinking water for human consumption, the degradation and detoxification of four of the most problematic MC variants, namely, MC-LR, -RR, -YR, and -LA, which differ in amino acid substituents, were evaluated using UV/chlorine and compared to results from chlorination. Overall, UV/chlorine effectively enhanced MC degradation kinetics and generated less halogenated disinfection byproducts in the target analysis of 11 types of DBPs_C