Water quality, lagoon safety, and beach conditions
📍 Ko Olina, West Oʻahu — Near Lagoons 3 & 4
Ko Olina's four engineered lagoons have excellent water quality. A year-long University of Hawaiʻi study found 88% of samples had zero detectable enterococci bacteria. This makes Ko Olina one of the cleanest swimming destinations on Oʻahu.
The JW Marriott Ihilani sits between Lagoon 3 (Naiʻa) and Lagoon 4 (Ulua) — both among the best-quality lagoons. Guests enjoy calm, protected swimming away from the open-ocean chop and Waikiki's urban runoff concerns.
Source: UH Water Resources Research Center 2019 Ko Olina lagoon study; DOH monitoring data
Ko Olina lagoons occasionally experience brownish water from dinoflagellate algae blooms (not bacteria — linked to fertilizer runoff from the resort). These are aesthetically unappealing but generally not a bacteria safety concern. Isolated bacteria spikes have also occurred — Lagoon 4 recorded elevated levels in November 2020.
Top-rated experiences near this beach. Check water quality above, then plan your trip.
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⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent project not affiliated with the Hawaii DOH or Marriott. Ratings are estimates — not real-time measurements.
Verify with the Hawaii DOH Clean Water Branch before swimming.
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. 🤙