HF183 is a DNA marker that is a particularly reliably indicator of human sources of fecal contamination in aquatic environments. The genetic marker is found in a type of gut bacteria known as Bacteroides spp.

HF183 was discovered during a landmark 2003 study examining different, then-experimental methods for detecting fecal contamination from different animal sources. The study – which included participation by the SMC – found that DNA-based methods like HF183 offer a consistently effective way to distinguish among different sources of bacteria. The finding was significant because fecal contamination indicators in use at the time were not able to distinguish human from nonhuman sources.

Since the 2003 study, researchers have further validated HF183 as a management tool for reliably detecting human-specific fecal sources. Today, HF183 is a foundational management tool that has become widely implemented to document human fecal contamination in waterways across southern California.