In the United States, thousands of creeks, rivers, and coastal zones are listed as impaired in the Clean Water Act's 303(d) list. The number one general cause of impairments is denoted as 'pathogens', which can include known pathogenic organisms or, more commonly, fecal indicator bacteria (FIB), such as fecal coliform bacteria, Escherichia coli, and enterococci bacteria. Despite efforts by water quality managers to reduce FIB in surface waters via treatment, successful and significant reduction of FIB has been difficult to achieve to meet water quality standards. In addition, current efforts to numerically model FIB concentrations in surface waters do not consider many complexities associated with FIB as a pollutant. Reasons for the challenge of treating and modelling FIB are their varied sources and mechanisms of survival and decay in the environment. This technical note addresses this challenge by discussing the nature of FIB, their sources, and their fate and transport mechanisms. Sources of FIB to surface waters include wastewater, stormwater and dry-weather runoff, and animals. Mechanisms of pathogen indicator occurrence in surface waters are transport in stormwater, ecological proliferation, and interaction with sediments.