Water quality samples are taken throughout the summer at population beaches throughout the Tahoe Basin. Samples are analyzed for the presence and concentration of Escherichia coli (E. coli). E. coli is considered an indicator organism, used to identify fecal contamination in freshwater and indicate the possible presence of disease-causing bacteria and viruses (pathogens). Individuals who swim or come in contact with water with elevated levels of E. coli and other fecal indicator organisms are at an increased risk of getting sick because of potential exposure to fecal pathogens (USEPA).