Enterococci bacteria, the 130 CFU threshold, and what it means for swimmers
Enterococci are a group of bacteria that naturally live in the intestines of humans and animals. They are not typically dangerous themselves, but their presence in ocean water is a strong indicator of fecal contamination — which means disease-causing pathogens may also be present.
The EPA recommends enterococci as the primary indicator for recreational saltwater quality because they survive longer in saltwater than other indicator bacteria (like E. coli) and correlate well with the risk of gastrointestinal illness in swimmers.
Sources of enterococci in Hawaiʻi’s nearshore waters include sewage spills, cesspool leakage, animal waste washed in by rain, and direct discharge from streams carrying bacteria from agricultural and urban areas.
DOH field staff collect water samples at designated monitoring stations along the beach. Samples are typically taken at ankle to knee depth in the surf zone. Multiple samples may be collected at different points along a beach.
Samples are transported to a laboratory and analyzed using EPA Method 1600, a membrane filtration technique. The water sample is filtered, and the filter is placed on a selective growth medium. After 24 hours of incubation at 41°C (106°F), enterococci colonies are counted. Results are reported as CFU (colony-forming units) per 100 milliliters.
If a single sample exceeds 130 CFU per 100 mL, DOH may post a beach advisory. The geometric mean of multiple samples must stay below 35 CFU per 100 mL. Advisories are posted on the DOH Clean Water Branch website and physically at affected beaches. Advisories are lifted when follow-up testing shows bacteria levels have returned below the threshold.
Not all Hawaiʻi beaches are tested for water quality. The DOH Clean Water Branch monitors a selection of recreational beaches, with testing frequency varying based on:
⚠ Key Limitation
Because testing takes 24 hours and sampling is not continuous, there is always a gap between water conditions and test results. A beach with “no advisory” may still have elevated bacteria — it may simply not have been tested recently. This is why visual assessment and the 72-hour rain rule are so important.
The single biggest factor. Rain washes bacteria, animal waste, and contaminants from land into nearshore waters via streams and storm drains.
Hawaiʻi has roughly 88,000 cesspools statewide that leach untreated sewage into groundwater, which eventually reaches the coast. Sewage line breaks also contribute to acute contamination events.
Animal operations and fertilizer use on farms contribute bacteria and nutrients that enter waterways during rain.
Feral animals (pigs, goats, chickens) and birds contribute fecal bacteria to streams and coastal waters. This is a significant source in rural and forested areas.
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⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent passion project — not affiliated with the Hawaii Department of Health or any government agency. Water quality ratings are estimates based on publicly available testing data. They are not real-time measurements.
Always verify conditions with the Hawaii DOH Clean Water Branch before entering the water.
When in doubt, don't go out. 🤙