Hanauma Bay, Sandy Beach, Makapuu — the volcanic southeast coast with less urban impact than Honolulu.
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Source: Hawaii DOH Clean Water Branch · Updated automatically
Hawaii Kai and the Southeast Oahu coast run from Maunalua Bay around the volcanic headlands of Koko Head and Makapuu Point. This is a transitional zone between urban Honolulu and the rural Windward Coast, with dramatically less development than downtown and Waikiki.
The geology here is dominated by the Koko Head volcanic series — relatively young eruptions that created the dramatic cliffs, Hanauma Bay crater, and the bluffs above Sandy Beach and Makapuu. This volcanic rock coastline has few streams and limited soil for runoff compared to the valleys of Windward Oahu.
Key contamination sources: Limited. Hawaii Kai marina (Kuapa Pond) runoff to Maunalua Bay, parking lot runoff at Hanauma Bay, and minor hillside drainage. No major streams or cesspools along the southeast coast beaches.
Source: NOAA climate normals; USGS stream data; Hawaii DOH CWB
Ranked by overall water quality risk. Dry weather baseline; all beaches see increased risk after rain.
Summer (May–September): Calm conditions, lower rainfall. Hanauma Bay at its clearest for snorkeling. Sandy Beach has smaller but still powerful shore break. Water quality is excellent across the area.
Winter (October–March): Slightly more rainfall but the southeast coast is drier than Windward Oahu. South and east swells can increase wave energy at Sandy Beach and Makapuu. Hanauma Bay remains relatively sheltered. Water quality is generally still good.
Key advantage: The Southeast Coast has the most consistent year-round water quality on Oahu because it lacks the major stream systems and urban drainage that affect other areas. The primary seasonal variable is wave energy, not water quality.
The Southeast Coast benefits from relatively low rainfall (20–30 inches annually) and minimal stream infrastructure. Rain impact is less severe here than on the Windward or North Shore coasts.
Hanauma Bay: Parking lot and hillside runoff can reach the bay after heavy rain, but the volume is small. Wait 24 hours after significant rain.
Maunalua Bay: The Hawaii Kai marina can discharge accumulated runoff. Avoid swimming near the marina outlet for 48 hours after heavy rain.
Sandy Beach & Makapuu: Virtually no runoff impact. Open ocean exposure means any minor runoff is quickly diluted. These beaches recover fastest on Oahu after rain events.
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Free alerts when advisories change on Oahu beaches.
Hawaii DOH Clean Water Branch — Beach monitoring, advisories. eha-cloud.doh.hawaii.gov
USGS — Stream gauge data, rainfall records.
NOAA / NWS — Climate normals, weather patterns.
⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent project — not affiliated with any government agency. Water quality assessments are based on publicly available data. They are not real-time measurements. Conditions change rapidly, especially after rain.
Always verify with the Hawaii DOH Clean Water Branch before entering the water.
When in doubt, don’t go out.