The number of colony-forming units (CFU) of bacteria belonging to the species Clostridium perfringens. Because this bacteria is a normal component of the human intestinal tract, its presence in samples of sea water can be used as a tracer of sewage contamination. As such, it is commonly measured in beach water quality monitoring programs.
The State of Hawaiʻi utilizes Clostridium perfringens as a secondary tracer in addition to the Enterococcus indicator to help distinguish between sewage and non-sewage sources of elevated Enterococcus levels in marine coastal waters. If Enterococcus concentrations remain elevated after resampling, a Clostridium perfringens concentration exceeding 50 CFU/100 mL requires a "Waste Water Condition" to be publicly posted.