Understanding flesh-eating bacteria risk, MRSA in coastal waters, and how surfers and swimmers can protect themselves.
This guide is for general informational purposes only and is not a substitute for professional medical advice. If you have health concerns related to water quality, consult a healthcare professional.
Vibrio vulnificus is a naturally occurring bacterium found in warm coastal and brackish waters worldwide. In Hawaiʻi, ocean temperatures consistently exceed 75°F, creating favorable conditions for Vibrio year-round. The bacteria is found in higher concentrations near estuaries, canal outlets, and areas where freshwater mixes with saltwater.
For the majority of healthy people, Vibrio exposure causes mild gastrointestinal symptoms at most. The danger is primarily to two groups: immunocompromised individuals (especially those with liver disease) who face life-threatening bloodstream infections, and anyone with open wounds exposed to contaminated water who may develop rapidly progressive wound infections.
Vibrio wound infections are a medical emergency. The bacteria enters through cuts, scrapes, or other breaks in the skin during ocean water exposure. Within hours, the wound area can become intensely painful, swollen, and red. Blisters may form. The infection can progress to necrotizing fasciitis — destruction of skin, fat, and muscle tissue — requiring emergency surgical removal of infected tissue.
If a wound becomes rapidly more painful, red, and swollen within hours of ocean exposure, go to the emergency room immediately.
Hawaiʻi has among the highest community-acquired MRSA (methicillin-resistant Staphylococcus aureus) rates in the United States. Studies have detected MRSA in nearshore waters, particularly in areas impacted by sewage contamination from cesspools and aging sewer infrastructure.
The Ala Wai Canal on Oʻahu is a focal point. This canal collects stormwater from a large urban watershed and frequently contains extremely high bacteria levels. When it overflows or discharges into the ocean near Waikiki, it delivers concentrated bacterial contamination to the nearshore waters. Surfers at spots near the canal outlet face elevated MRSA exposure, particularly after rain events.
The Ala Wai Canal was built in the 1920s to drain the wetlands that became Waikiki. Today it serves as the primary stormwater drainage channel for one of the most densely developed areas in Hawaiʻi. The canal collects runoff from roads, parking lots, golf courses, and residential areas — including areas with aging sewer lines and cesspools.
In 2006, a man died from Vibrio-related septicemia after falling into the Ala Wai Canal. The incident highlighted the extreme contamination levels in the canal and the risk that this contamination poses to ocean water quality when the canal discharges into the ocean.
After heavy rain, the canal overflows and discharges contaminated water directly into the nearshore ocean. This is the primary reason that Waikiki beaches receive brown water advisories after storms and why bacteria levels near the canal outlet are consistently higher than at beaches farther from the discharge point.
Top-rated experiences across Hawaiʻi.
Tours listed via Viator and GetYourGuide. Safe to Swim Hawaii may earn a commission if you book, at no extra cost to you.
Free alerts when water quality changes at your beach.
No spam. Just safety alerts for your trip.
Safe to Swim Hawaii aggregates water quality data from six independent sources to provide broader coverage than any single agency. Our sources include the Hawaii Department of Health Clean Water Branch (beach advisories and bacteria testing), USGS National Water Information System (25 stream monitoring stations across all islands), NOAA CO-OPS (tide levels and water temperature), NDBC (wave buoys and ocean conditions), NWS Honolulu (weather and marine alerts), and City & County of Honolulu Environmental Services (Kailua Bay water testing and spill reports).
Historical bacteria risk ratings on this site are based on DOH testing data, Surfrider Foundation monitoring, geographic analysis (stream proximity, cesspool contamination areas, coastal development), and advisory frequency. These are historical assessments, not live measurements. Always check the live advisory status at the top of each page and verify conditions with the Hawaii DOH Clean Water Branch before entering the water.
⚠️
Safe to Swim Hawaii is an independent passion project — not affiliated with the Hawaii Department of Health. This page provides general health information and is not medical advice.
Always verify current water quality with the Hawaii DOH Clean Water Branch before entering the water.
This site does not recommend or advise anyone to swim at any beach. We share government data and geographic analysis so you can make your own informed decisions. By using this site you accept full responsibility for your own safety. See our Terms of Use for full details.
When in doubt, don't go out. 🤙
Less rainfall means less runoff and generally cleaner ocean water across all islands. Stream flows drop, reducing bacteria transport to coastal areas. This is typically the best time for ocean water quality, though localized contamination from cesspools and urban runoff can still occur.
Frequent heavy rain events cause stream flooding, sewage overflows, and brown water advisories. Windward and north-facing coasts receive more rain. The DOH issues the most advisories during this period. Leeward coasts (west-facing) generally stay drier and cleaner year-round.
Water quality patterns vary significantly by location. Beaches near stream mouths and urban areas show the most dramatic seasonal variation. Open ocean beaches with strong wave action maintain better water quality year-round. Check individual beach pages for location-specific seasonal data.
Hawaii has approximately 88,000 cesspools — more than any other U.S. state. These underground chambers collect untreated household sewage and allow it to leach into the surrounding soil and groundwater. In coastal areas, this contaminated groundwater eventually reaches the ocean through submarine groundwater discharge, contributing to elevated bacteria levels at nearby beaches.
Hawaii Act 125 (2017) requires all cesspools to be upgraded or converted to approved septic systems by 2050. Priority areas near the coast and drinking water sources are being addressed first, but progress has been slow. Beaches in known cesspool contamination zones carry elevated bacteria risk even during dry weather. For more information, see our comprehensive cesspool guide.
Safe to Swim Hawaii checks water quality data every 15 minutes from multiple government agencies. When conditions change — a new advisory is posted, stream levels spike after rain, or an advisory is cancelled — our pages update automatically. This means you are seeing the latest available data from official sources, not a static snapshot.
The Hawaii Department of Health Clean Water Branch operates the state’s official beach monitoring program. Tier 1 beaches are tested weekly; Tier 2 beaches are tested less frequently. When bacteria levels exceed 130 enterococci per 100 mL, the DOH issues a Beach Advisory for that location. Brown Water Advisories are issued based on visual assessment of runoff conditions, not bacteria testing.
USGS stream monitoring stations measure water flow (discharge) and turbidity in real time. When a stream near a beach is flowing at 5x or more above its normal rate, this indicates significant runoff that likely carries elevated bacteria. We display these stream conditions alongside DOH advisories to give a more complete picture of water quality at each beach.