Island-by-island grades based on advisory frequency, bacteria test results, and contamination sources. We graded every major island so you can choose the cleanest coastline for your trip.
Grades are based on three factors weighted together: DOH advisory frequency, bacteria test failure rates, and severity of contamination sources in each island’s watershed.
| Grade | Advisories/Year | Meaning |
|---|---|---|
| A | 0–1 | Consistently clean. Minimal contamination sources. Low bacteria test failure rates. |
| B | 2–3 | Occasional issues, typically seasonal. Generally acceptable water quality. |
| C | 4–6 | Seasonal problems. Multiple contamination sources. Elevated failure rates at some stations. |
| D | 7+ | Chronic issues. Frequent advisories. Significant contamination infrastructure. |
| F | Persistent | DOH-impaired designation. Contamination exceeds standards year-round. |
Grades are based on DOH monitoring data supplemented by Surfrider Blue Water Task Force and community monitoring programs. Individual beaches within each island can vary significantly from the island average.
The Kohala Coast on the Big Island’s west side is the gold standard for Hawaiʻi water quality. Dry climate, no streams near resort beaches, modern wastewater systems, and strong ocean circulation keep bacteria levels at the lowest in the state. Hapuna Beach, Mauna Kea Beach, and Mauna Lani Bay rarely if ever trigger advisories.
The exception: Kahaluʻu Beach Park in Kailua-Kona has a 92% bacteria test failure rate — the worst of any monitored beach in Hawaiʻi. UH Hilo research confirmed cesspool wastewater reaching the shoreline. This single beach is why the Big Island gets an A- instead of a solid A.
The Hilo side receives heavy rainfall (130+ inches/year) but has fewer popular swimming beaches. Water quality on the east coast is weather-dependent.
South Maui (Wailea, Kīhei, Makena) is the driest coast in the state and consistently has excellent water quality. Minimal streams, modern infrastructure, and strong ocean circulation keep bacteria low year-round.
West Maui (Kaʻanapali, Kapalua) has seen increased water quality scrutiny since the 2023 Lahaina fire. Exposed soil, damaged infrastructure, and debris runoff have raised concerns about post-storm contamination. Hanakaoo Beach Park near Kaʻanapali has shown chronic bacteria issues regardless of season.
North Shore and East Maui (Paʻia, Hana) receive heavy rain and have more variable water quality but fewer popular swimming beaches.
Kauaʻi has the most extreme contrast of any island. Poipu Beach on the dry south shore has excellent water quality year-round. But the north shore includes some of the most contaminated beaches in the state.
Hanalei Bay has been DOH-impaired since 2004 — the longest-standing impairment designation for any beach in Hawaiʻi. Four river discharges and over 360 cesspools in the watershed create chronic contamination. Kalapaki Beach near Līhuʻe has chronic bacteria contamination at the stream mouth.
Kauaʻi also receives the most rainfall of any major island, which drives more frequent Brown Water Advisories. The interior includes Mt. Waiʻaleʻale, one of the wettest spots on Earth.
Oʻahu has the highest advisory count of any Hawaiian island. Urban density, the Ala Wai Canal system, aging wastewater infrastructure, and the highest cesspool concentration in residential areas create multiple chronic contamination sources.
The North Shore has chronic bacteria issues near stream mouths (Halʻeiwa, Waimea Bay). Heavy winter rain drives elevated bacteria from November through March. Ala Moana Beach Park near the Ala Wai Canal outflow has chronic issues regardless of season.
Bright spots: The south shore (Waikiki east end near Diamond Head) tests relatively clean during dry weather. Ko Olina Lagoons on the west side perform well year-round — no streams, self-flushing lagoons, and the dry leeward coast. Windward Kailua Beach (south end, away from Kawainui Marsh outlets) generally tests clean during dry periods.
Waikiki is Hawaiʻi’s most visited beach, so this question comes up constantly. The answer is: it depends on which end and recent weather.
The eastern end of Waikiki (near Diamond Head and the Waikiki Aquarium) generally tests cleaner. It is farthest from the Ala Wai Canal outflow and has better ocean circulation.
The western end (near the Hilton Hawaiian Village and Ala Wai Canal) receives the most direct impact from canal discharge. After rain, bacteria levels spike significantly at this end before the eastern stations are affected.
During extended dry weather, most Waikiki monitoring stations test within acceptable limits. After any significant rain, give it at least 72 hours and check our Waikiki page for current conditions.
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⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent project — not affiliated with the Hawaii Department of Health or any government agency. Beach grades are our assessment based on publicly available data and should not be interpreted as official ratings. Individual conditions vary daily. Always verify current water quality with the Hawaii DOH Clean Water Branch before entering the water.
When in doubt, don’t go out. 🤙