The accumulation of bacterial biofilms and consequent clogging of screens, pipes, and heat exchanger equipment is problematic for water supply systems contaminated with iron bacteria and other slime forming bacteria. Despite the ubiquitous threat posed by iron bacteria contamination in groundwater sources, limited research has focused on physical treatments to address this issue. We sought to investigate the effectiveness of ultraviolet (UV) irradiation on inactivating iron bacteria and slime forming bacteria in a fish hatchery supply water known to have issues with bacterial biofilms. Biological activity reaction tests (BART) were used to analyze the presence or absence of iron related and slime forming bacteria in raw well water at UV dosages of 0 mJ/cm2, 15 mJ/cm2, 30 mJ/cm2, 45 mJ/cm2 and 60 mJ/cm2. Results suggest that UV treatment decreases iron bacteria survival, with the highest percent of non-reactive BARTTM test vials resulting from 45 mJ/cm2 and 60 mJ/cm2 UV exposure; however, data regarding UV inactivation of slime forming bacteria were inconclusive. These initial ‘proof of concept’ findings can be used to design pilot UV water treatment systems for fish hatcheries known to have iron bacteria problems. Pilot treatment system testing can then provide the necessary results to ensure that UV treatment is effective against site-specific iron bacteria populations before full-scale treatment systems are implemented.