Big Island vs Maui vs O'ahu vs Kaua'i ranked by days advisory-free in the last 30 days, using live Hawaii Department of Health data. For trip planners who haven't picked an island yet.
Kaua'i ranks #1 this month with 63.3% advisory-free days across 6 tracked beaches. O'ahu is currently #4 at 41.4%.
The percentage for each island is (advisory-free beach-days ÷ total beach-days) × 100, measured over the last 30 days across our tracked set of beaches on that island. A day counts as "under advisory" if the beach had any active DOH Beach Advisory (bacteria exceedance) or Brown Water Advisory (runoff) on that day.
Sample-size caveat: we currently track 7 on the Big Island, 6 on Maui, 6 on Kaua'i, and 12 on O'ahu — 31 total. That is not a representative sample of every swimmable beach in the state; it is a concentrated sample of locations with usable advisory history. The percentages are directionally informative but will sharpen as the tracked set expands.
What it is not: a swim-safety rating. An island can rank high here but have beaches with strong currents, large surf, or no lifeguards. Water quality is one of several factors. Always check the individual beach page for physical-hazard context and the live DOH status before you swim.
Geography drives these numbers more than any local factor. Three patterns repeat across every monthly snapshot:
For water quality alone, the hierarchy is reliable across months: Big Island → Maui → O'ahu/Kaua'i. The Big Island's Kohala Coast is the lowest-risk choice. South Maui (Wailea, Makena, Kapalua) is close behind and offers more variety.
If you want the best swimming conditions + the lowest advisory risk — book the Big Island's Kohala Coast or South Maui.
If you want North Shore O'ahu or Kaua'i's north shore for other reasons (surfing, scenery, hiking) — go in summer (May–September), when the storm track moves north and those coasts dry out. Winter trips to those coasts carry real advisory risk.
If you want O'ahu for convenience or budget — the Ko Olina lagoons and the east end of Waikiki (Sans Souci) are the best-bet zones. The Ala Wai Canal affects central Waikiki after rain.
Once you've picked an island, our cleanest Hawaii beaches leaderboard drills down to the individual beach level across the state. Each beach has its own page with a 30-day daily-bar chart showing exactly which days had advisories.
Built from the Hawaii DOH Clean Water Branch public API (Beach Advisory + Brown Water Advisory events, including bacteria Count values when an advisory is issued), the DOH monitoring station registry, and the EPA Recreational Water Quality Criteria (130 CFU/100 mL enterococcus threshold). Updated daily.
Based on the last 30 days of DOH advisory data, Kaua'i ranks #1 at 63.3% advisory-free beach-days in this tracked sample. This describes posted advisories, not direct water testing or a swimming-safety guarantee.
Yes, significantly. Winter / spring (Nov–Apr) is the wet season for most of Hawaii. Kona Lows and large storm systems drive up Brown Water Advisory frequency. Summer (May–Sep) typically shows much cleaner numbers across the board. The Big Island's Kohala Coast stays clean year-round because it is in a persistent rain shadow.
No. The ranking compares the frequency of posted DOH advisories in this tracked sample; it does not directly measure all bacteria conditions or swimming safety. Physical hazards like shore break, rip currents, seasonal large surf, and absence of lifeguards are not included. Always check the individual beach page and current DOH status before swimming.
We pull every Beach Advisory and Brown Water Advisory issued by the Hawaii DOH in the last 30 days. For each tracked beach, we count days under any advisory. For each island, we aggregate across all tracked beaches on that island. The percentage is (advisory-free beach-days ÷ total beach-days) × 100. Refreshes daily.