UH research tested Ko Olina’s lagoons for a full year. Waikiki faces urban runoff and the Ala Wai Canal. Here’s what the data shows.
Ko Olina’s engineered lagoons have dramatically better water quality than Waikiki. A University of Hawaii Water Resources Research Center study tested all four Ko Olina lagoons for 12 months in 2019 and found that 88% of samples had zero detectable enterococci bacteria. Only 1 of 128 samples exceeded the state health threshold.
Waikiki faces different challenges: urban stormwater runoff, the Ala Wai Canal discharge, and high visitor density. These are manageable most of the time, but the risk profile is higher — especially after rain.
Ko Olina’s four lagoons (Kohola, Honu, Nai’a, and Ulua) are man-made swimming areas carved from the rocky leeward coastline. They sit on O’ahu’s dry west side with no streams, no canal discharge, and no urban runoff pathways. The leeward coast receives roughly 17–20 inches of rain annually.
The UH Water Resources Research Center study collected 128 water samples across all four lagoons from January to December 2019. Key findings: enterococci were not detected in 88% of samples. Only one sample exceeded the 130/100mL Beach Action Value, and that sample tested negative for human-associated Bacteroides markers — meaning the source was environmental (soil, wildlife), not human sewage.
Source: UH WRRC Special Report SR-2020-04, “Microbiological Water Quality of Ko Olina Lagoons”
Waikiki is Hawaii’s most famous beach but it sits in an urban environment with specific water quality challenges. The Ala Wai Canal runs along the northern edge of the Waikiki strip and discharges near the western end (Hilton Hawaiian Village area). During rain, urban stormwater carries pollutants from streets, parking lots, and landscaping into the canal and ocean.
Kahanamoku Beach (fronting the Hilton) recorded 150 enterococci per 100mL in March 2020. During May 2024, Kuhio Beach had a bacteria exceedance but DOH didn’t conduct follow-up testing because an island-wide brown water advisory was in effect — a testing gap that Civil Beat reported on and Surfrider lobbied to change. Historical DOH data rated Fort DeRussy and Kuhio Beach as having “poor” water quality.
To be fair: Waikiki is a DOH Tier 1 priority with weekly testing at multiple sites. When problems arise, they’re detected and reported. Ko Olina has less regular state monitoring, which means issues could go undetected longer.
Source: DOH CWB advisories; Civil Beat (May 2024); DOH 1992 marine recreational water assessment
Ko Olina has had its own issues:
Ulua Lagoon 4 — November 2020: Recorded 429 enterococci per 100mL (3x the safe limit). This is the lagoon fronting Marriott’s Ko Olina Beach Club.
Kohola Lagoon 1 — January 2017: Brief exceedance detected at the lagoon fronting Disney’s Aulani and Four Seasons. Signs posted and removed within a day after follow-up testing came back clean.
Dinoflagellate blooms: The UH study documented algae blooms (tentatively Gymnodinium) in two lagoons that caused brown water appearance. These are not bacteria-related — they’re algae linked to elevated nitrogen from resort irrigation and fertilizer. Saxitoxin levels were low and not a health risk.
2011 landfill event: Waimanalo Gulch Landfill flooded during heavy rains and sent debris, including medical waste, onto Ko Olina beaches. This was an extreme one-time event; all lagoons were closed and subsequently cleared.
Source: DOH CWB advisories (Honolulu Star-Advertiser Nov 2020, KHON2 Jan 2017); UH WRRC 2020; Star-Advertiser Jan 2011
All four lagoons share similar excellent water quality profiles:
Water quality varies along the 2-mile Waikiki strip. Distance from the Ala Wai Canal matters:
Book Ko Olina. The lagoons offer the cleanest resort swimming on O’ahu. The trade-off: you’re 30–40 minutes from Honolulu and the energy of Waikiki.
Waikiki is safe to swim most of the time during dry weather. Key tips:
• Avoid swimming for 72 hours after heavy rain. The Ala Wai Canal and storm drains flush pollutants to the shoreline. See our rain safety guide →
• Central Waikiki (Royal Hawaiian area) generally tests cleaner than the Hilton end or Kuhio Beach end.
• If water looks brown or murky, don’t go in — regardless of whether signs are posted.
• Check for active advisories at the DOH Clean Water Branch.
Ko Olina wins on water quality, but Waikiki wins on monitoring. Waikiki has DOH Tier 1 weekly testing at multiple sites, plus Surfrider supplemental testing. Ko Olina has less regular government monitoring — the UH study was a research project, not an ongoing program. If something goes wrong at Ko Olina, it could take longer to detect.
UH Water Resources Research Center — “Microbiological Water Quality of Ko Olina Lagoons” (SR-2020-04), 128 samples, Jan–Dec 2019. wrrc.hawaii.edu
Hawaii DOH Clean Water Branch — Tier 1 beach monitoring, advisories. eha-cloud.doh.hawaii.gov
Surfrider O’ahu — BWTF 2024 Report, 26 sites bi-weekly. oahu.surfrider.org
Civil Beat — “Hawaii Moves To Improve Water Testing At Popular Beaches” (May 2024).
⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent passion project — not affiliated with any government agency or monitoring organization. Assessments are based on publicly available data. They are not real-time measurements. “No DOH Alerts” means no advisory is currently posted — it does not mean the water was tested and found safe. DOH only monitors a fraction of Hawaii’s beaches, and some areas have no regular testing at all.
Always verify current conditions with the Hawaii DOH Clean Water Branch before entering the water.
When in doubt, don’t go out. 🤙