Excessive algal growth in drinking water sources like lakes and reservoirs is responsiblefor filter-clogging, undesirable taste and odor, disinfection-by-product formation and toxingeneration. Although various methods are currently being used to control algal bloom, theirsuccesses are limited. Many water utilities routinely use copper sulfate to control excessive algalgrowth. But there is a growing concern against its use mainly because it is non-specific to targetalgae and kills many non-target species. In this study, the scope of using UV-radiation to controlalgal growth was assessed using Microcystis aeruginosa and Anabena vulgaris as test species. Forboth of these species, an incident UV-dose of 450-m Ws/cm2 was found to be lethal. A smaller doseof 180-m Ws/cm2 prevented growth for about 7-days. It was also observed that UV-radiation onalgal extracellular products has a significant residual effect and can contribute to algal growthcontrol. The extent of residual effect depends on the UV-dose and can continue even for 7-days.