Oʻahu has 40+ monitored beaches tracked by the Hawaii Department of Health every 15 minutes. West shore (Ko Olina) has low long-term advisory exposure. South shore (Waikiki) is affected by Ala Wai Canal runoff after rain. Windward Coast (Kailua, Lanikai) can be lower-caution in dry weather. North Shore has large winter surf.
Live DOH advisories · brown water alerts · beach warnings · rain/runoff guidance
Start with water quality, then check surf and weather. The live DOH box below is the current status; if it names an Oʻahu event, read the affected-water language before treating a whole coast as clear. Ko Olina’s four sheltered lagoons on the leeward west side usually have lower runoff exposure. South Shore (Waikiki, Ala Moana) is affected by Ala Wai Canal discharge after rain. Windward (Kailua, Lanikai) can look clear in dry weather but changes quickly after storms. Use the shortcut after the live box to jump to the exact beach, current alert list, or after-rain picker.
Use the live DOH box first, then choose the Oʻahu route that matches your plan: a current advisory, Waikiki and Ala Wai runoff, windward Kailua or Lanikai, North Shore river mouths, leeward lagoons, or after-rain timing.
Oʻahu is home to roughly 84% of Hawaii's hotel rooms, meaning most visitors swim on this island's beaches. Water quality varies dramatically depending on where you are and when it last rained.
The Ala Wai Canal is the single largest contamination source on Oʻahu's south shore. It drains a 19-square-mile urban watershed — carrying sewage overflows, storm runoff, motor oil, and trash — and discharges directly into the ocean between Waikiki and Ala Moana. After any significant rain, bacteria levels near its outlet spike well above DOH bacteria thresholds.
The windward coast (Kailua, Lanikai) receives more rainfall and has marshland drainage that elevates bacteria after storms. The leeward and west side (Ko Olina, Makaha) is drier with fewer stream mouths, generally resulting in cleaner water. The North Shore has seasonal surf that stirs up sediment plus multiple stream outlets that carry runoff during winter rains.
Exploring Oʻahu? These top-rated tours and activities pair perfectly with a beach day. Check water quality above, then plan your trip.
Tours listed via Viator and GetYourGuide. Safe to Swim Hawaii may earn a commission if you book, at no extra cost to you.
Beach water quality reports for popular Oʻahu hotels — check conditions at your resort.
DOH only tests roughly 47 stations across the four main islands. Surfrider Foundation’s volunteer Blue Water Task Force adds 100+ community-tested sites on Oʻahu, Maui, and Kauaʻi. Molokaʻi and Lānaʻi still have no routine bacteria-testing program, so we separate that gap clearly.
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⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent passion project — it is not affiliated with the Hawaii Department of Health or any government agency. Water quality ratings on this site are estimates based on publicly available testing data and geographic analysis. They are not real-time measurements and may not reflect current conditions. “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 water quality conditions with the Hawaii Department of Health Clean Water Branch before entering the water. This site is for informational purposes only and should not be the sole basis for any swimming decisions.
This site is a work in progress and we want to make it better. If you notice something that isn't working right, have a suggestion, or want to share local knowledge about a beach, please reach out.
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. 🤙
Page last updated June 11, 2026. Live advisory data refreshes from the Hawaii DOH feed every 15 minutes.