The enumeration of phages infecting host-specific strains of Bacteroides has been widely recognised as an effective and low-cost method of microbial source tracking (MST). A recently described human-specific Bacteroides host strain (GB-124) has been shown to detect bacteriophages exclusively in human-impacted waters and is emerging as a useful MST tool. However, a better understanding of the morphology and ecological behaviour of the phages, especially in wastewater disinfection processes, is now required in order to validate their role as MST markers. Bacteriophages infecting Bacteroides fragilis GB-124 (n = 21) were isolated from wastewater effluent and irradiated using laboratory-based UV-C (254 nm) collimated beam experiments. Bacteriophages were found to be both a morphologically and ecologically homogeneous group, with all specimens showing highly similar first order log-linear inactivation profiles (mean fluence required to inactivate phages by 4-log(10) was 36 mJ/cm(2)). These findings present the first evidence that phages infecting GB-124 are inactivated by the levels of UV-C radiation routinely delivered during tertiary wastewater treatment processes. More importantly, comparison with previously published inactivation data suggests that their response to UV-C radiation makes GB-124 phages more suitable surrogates for selected enteric viruses in UV disinfection processes than traditional faecal indicator bacteria or human-specific molecular markers.