Exposure to sewage contaminated recreational waters may cause gastrointestinal illnesses in swimmers. The State of Hawaii Department of Health (HIDOH) Clean Water Branch (CWB) monitors the waters of Hawaii's beaches for concentrations of Enterococcus, which acts as an indicator of pathogens. The CWB also uses Clostridium perfringens as a secondary tracer of sewage contamination. Results of this monitoring are evaluated using a decision rule to determine whether a beach is safe ("Compliant") or not safe (on "Alert") for swimming and other water contact activities. If a beach is found to be on "Alert" due to elevated indicator bacteria levels, the CWB issues public warnings and alerts and determines whether resampling of the area is necessary.

Under the U.S. BEACH Act, the State of Hawaii receives an annual grant to implement its beach monitoring program. This requires the State to conduct a monitoring and notification program that is consistent with performance criteria published by the U.S. Environmental Protection Agency (EPA) in 2002. In March 2010, the EPA approved amendments to the Hawaii Administrative Rules (HAR), Chapter 11-54, Water Quality Standards (CWB QAPrgP, HIDOH 2011, Appendix D), which revised the previous State Enterococcus criteria of a geometric mean (GM) of 7 colony-forming units (CFU) per 100 mL and a single sample maximum (SSM) of 100 CFU/100 mL to meet current EPA guidelines. The State of Hawaii now uses the EPA recommended Enterococcus GM and SSM for recreational waters consistent in the 1986 Ambient Water Quality Criteria for Bacteria. The criterion lists the GM and SSM for marine waters as 35 CFU/100 mL and 104 CFU/100 mL, respectively.

The CWB 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. The reliability of Enterococcus as an indicator organism in tropical environments has been questioned. This issue was formally documented in the report, Tropical Water Quality Indicator Workshop (Fujioka and Byappanahalli, 2003).

One of the limitations of all available and EPA-approved test methods is that the sample must be incubated for about 24 hours. As a result, the public finds out today when they shouldn't have gone in the water yesterday. As a result, warning signs on the beach may or may not be reflective of actual water quality because they are based on tests performed one or more days ago.