The Alfred Merritt Smith Water Treatment Plant (AMSWTP) supplies 85% of the required drinking water for the Las Vegas Valley. The potable water supply for the AMSWTP is Lake Mead, which is part of the Colorado River system. Four major waterways carrying untreated urban runoff from the Las Vegas Valley enter into Lake Mead via the Las Vegas Wash. Recognizing that the valley's urban runoff is a nonpoint source of pollution to the potable water supply the AMSWTP initiated a pathogen virus monitoring program from November 2000 to November 2001. The strategy of this program was to sample the 4 waterways on a monthly basis and then analyze the samples by a combined ICC-RT-PCR method. The targeted viruses were those already being monitored for in Lake Mead: enterovirus; hepatitis A virus; norovirus genotype I and II and group A rotavirus. Sample processing methods, elution and concentration, established during the virus ICR study, were also used. Results from the project revealed that in 9 of the 12 months during the project period either rotavirus or enterovirus was detected. Also, all of the waterways during the testing produced positive results for rotavirus or enterovirus. Neither hepatitis A virus nor norovirus was detected during this time period. Includes 20 references, tables, figures.