Short answer: check the current DOH advisory for the exact beach and stay out of affected water while a notice is active. After heavy rain, DOH recommends avoiding affected water for 48–72 hours after rain stops and the beach receives full sunshine. This precaution is not an all-clear: elapsed time, clear-looking water and a dry coast do not establish current water quality.
Page last updated: September 13, 2026
| Situation | Next step | Coastal context |
|---|---|---|
| Light shower Rain near your beach |
Check advisories | A brief shower or a sunny coast cannot rule out upland runoff or an active notice. Avoid stream mouths. |
| Visible runoff Brown or murky water |
Stay out | Stay out of brown or murky water even if no advisory is posted. Clear appearance is not proof of water quality. |
| Heavy storm 48–72 hour rule |
48–72 hr precaution | Count from rain stopping and full sunshine at the beach. An active DOH advisory still applies after this precautionary period. |
| Kona low / prolonged Multi-day soaking rain |
Follow current notices | Prolonged rain can prolong runoff. No fixed number of days clears a beach, including sheltered bays and leeward coasts. |
Current conditions control: stay out of affected water during an active advisory, and out of brown or murky water even without a notice. Clear-looking water does not establish safety.
Sources: DOH Beach Monitoring Program and DOH heavy-rain precautions, August 17, 2026. Check current DOH notices for the affected area.
DOH recommends a 48–72 hour precaution after heavy rain stops and the beach receives full sunshine. It does not clear an active advisory. Check the exact beach’s current DOH notice and local conditions; stay out of brown or murky water.
No. Hapuna, Wailea, Ko Olina, Poipu, and Makena have different coastal settings, but none has a guaranteed recovery time. Their current advisories and local conditions still control.
A light shower alone does not establish whether to enter the water. Upland runoff can reach a beach that looks sunny, and an earlier advisory may still be active. Check current DOH notices, avoid affected water, and stay out if the water is brown or murky.
Choose your island, where it rained, and when it stopped to review beach-planning context. Always check current DOH advisories and local conditions; a planning tool does not clear the water.
After heavy rain, follow DOH precautions and current advisories. Stormwater can carry sewage, animal waste, chemicals and debris into the ocean through streams and storm drains. Water can look clear while carrying runoff risk. The 48–72 hour precaution after rain stops and full sunshine is not permission to enter water covered by an active notice.
If the water looks brown or murky, stay out even without a posted notice. Runoff can affect stream mouths, drains and sheltered water near Kailua Beach, Waikiki and other coasts. A dry location does not rule out contamination. Review the island guides below.
Hawaii has approximately 88,000 cesspools that discharge an estimated 52 million gallons of undertreated sewage into the ground and coastal waters every day. When it rains, this sewage — along with animal waste, agricultural chemicals, fertilizers, motor oil, and urban debris — gets flushed through streams and storm drains directly into the ocean.
The result is the “brown water” that gives Hawaii’s brown water advisories their name. But the visible discoloration is mostly dirt and sediment. The real danger is invisible: enterococcus and other fecal indicator bacteria that can cause gastrointestinal illness, skin rashes, ear infections, eye infections, and wound infections.
A brown water advisory concerns runoff that can contain pollutants beyond the bacteria indicator used in routine monitoring. A missing sample does not establish clean water. The September 2024 Hawaii DOH program document lists about 407 BEACH Act beaches statewide and reports that about 167 were monitored in 2023; frequency varies by tier and resources.
The Surfrider Foundation conducted a 3-year study tracking over 10,000 surf sessions in San Diego. They found that illness rates were highest during rain and the first day after, then declined steadily, reaching near-baseline levels after 72 hours. That research is the basis for the widely-cited 72-hour rule.
However, a UCLA study analyzing 7 years of water quality data found that bacteria levels can remain elevated for up to 5 days near storm drains and creek outlets. For beaches with these features, a longer wait may be appropriate.
Open-ocean beaches on dry coasts, away from streams: coastal setting can influence exposure, but it cannot predict a clearance time. Follow the same current-advisory and heavy-rain precautions.
Beaches near stream mouths or storm drains: avoid runoff and affected water. Upland rain can matter even when the beach is sunny. Do not use elapsed time to overrule a notice.
Enclosed bays or breakwater-protected beaches: calmer waves do not establish water quality. Check current notices for locations such as Ala Moana and Kahalu’u Beach Park.
Freshwater streams and ponds: The DOH warns against entering freshwater after any rain due to leptospirosis risk, a serious bacterial infection that can be fatal. This applies to waterfall pools, river crossings, and any standing freshwater.
Hawaii has two seasons, not four. The wet season runs from roughly November through March, with December through February typically being the rainiest months. The dry season runs from May through October. The transition months of April and October can go either way.
The majority of brown water advisories and bacteria exceedances happen during wet season. But rain in Hawaii is extremely localized — it can be pouring on one side of an island while the other side is sunny and dry.
Every Hawaiian island has a wet side (windward — north and east, facing the trade winds) and a dry side (leeward — south and west, sheltered by the mountains). The rainfall difference is enormous: Hilo on the Big Island’s windward coast gets 10 to 40 times more rain than the Kona resort coast just 50 miles away.
This means choosing the right coast matters more than choosing the right month. A leeward beach during wet season can be drier and cleaner than a windward beach during dry season.
These destination pages include current notices and coastal context. A dry coast or an absence of visible streams does not establish water quality after rain.
These beaches sit near stream mouths, have chronic cesspool contamination, or sit in enclosed bays where runoff lingers.
Best months: May–October. The south shore (Waikiki) is generally drier, but Ala Moana has chronic issues from the Ala Wai Canal regardless of season. The North Shore gets heavy winter rain and surf. Ko Olina’s man-made lagoons exchange water with the ocean, but that does not rule out runoff or an active advisory.
Best months: May–October. South Maui (Wailea, Makena) is generally drier than windward Maui; that is climate context, not a current water-quality result. West Maui (Ka’anapali, Kapalua) gets more winter rain but is still significantly drier than east Maui. Hanakaoo near Ka’anapali has shown worsening bacteria trends regardless of season.
Best months: May–September. Kaua’i gets more rain than any other island. The south shore (Poipu) is generally drier than the north shore, but island-wide advisories still apply. Hanalei Bay on the north shore has been DOH-impaired since 2004 — wet season makes it worse, but the underlying cesspool problem exists year-round. Kalapaki near Lihue has recorded repeated enterococcus exceedances in BWTF community testing.
Best months: Any — the Kona coast is dry year-round. Hapuna Beach on the Kohala Coast has a dry coastal setting, but seasonal geography does not establish its current water quality. The Hilo/east side is one of the wettest places on earth and should be avoided for swimming after any rain. Kahalu’u in Kona has confirmed cesspool contamination that worsens after rain.
Hawaii DOH Clean Water Branch — The official source for active brown water advisories, beach advisories, and sewage spill notifications. Visit the DOH CWB website →
Safe to Swim Hawaii — This site pulls DOH advisory data every 15 minutes and combines it with historical bacteria testing data and risk ratings for 100+ beaches and 25+ hotels across all islands. Check your beach →
Visual inspection — If the water looks brown, murky, or discolored, don’t go in. This applies even when no advisory has been issued. If you can see a stream flowing brown water into the ocean, stay well away from the mixing zone.
No beach has a guaranteed recovery schedule. Review current DOH notices and local conditions for the exact destination; geography and time since rain are context, not clearance.
Rainfall, runoff routes and ocean circulation vary by place and storm. The table describes coastal context, not a recovery forecast. Check the exact beach’s current DOH notice before making a plan.
| Area | Coastal context |
|---|---|
| North Shore O’ahu | Waimea River and Haleiwa stream carry heavy upland runoff. Waimea Bay sits right at a river mouth. |
| Waikiki | The Ala Wai Canal collects runoff from the entire valley behind Waikiki and dumps it at the west end of the beach. |
| Kailua | Kailua Beach receives runoff from Kawainui Marsh, one of the largest wetlands in Hawaii. Stream outlets at both ends of the beach. |
| Ko Olina | Man-made lagoons on a leeward coast. A sheltered setting does not exclude runoff or island-wide advisories. |
| Maui South Shore Wailea / Kihei |
Wailea is on Maui’s generally drier south coast. Check current advisories; dry-coast geography does not establish recovery. |
| Maui West Side Ka’anapali / Lahaina |
Multiple stream outlets along the coast. Hanakaoo has shown chronic bacteria issues. Kapalua Bay is sheltered, which does not establish its current water quality. |
| Kaua’i North Shore Hanalei / Princeville |
One of the wettest places on earth. Hanalei Bay has 4 streams and 360+ cesspools. DOH-impaired since 2004. |
| Kaua’i South Shore Poipu |
Poipu sits on the dry leeward coast with minimal stream influence and strong ocean circulation. |
| Big Island Kohala Coast Hapuna / Kua Bay |
Hapuna and Kua Bay are on the generally dry Kohala coast. Storm runoff and current advisories can still affect this coastline. |
| Big Island Hilo Side | Hilo gets 130+ inches of rain per year. Constant streams, rivers, and waterfalls feed the coast. Avoid swimming after any rain on this side. |
Sunshine and ocean circulation influence environmental conditions, but neither establishes that pollutants are gone. A current advisory continues to apply until DOH lifts it.
The 72-hour rule is the most cautious end of the commonly cited 48–72 hour rain window. Surfrider Foundation research tracking surfer illness found risk declined after the first several days, but that research measured average conditions at average beaches after moderate rain. Hawaii has unique factors that can push the lower-risk window well beyond three days.
A Kona low is a subtropical weather system that reverses normal wind patterns and dumps heavy rain on normally dry leeward coasts. Unlike typical trade-wind showers, Kona lows can drop several inches across an entire island over multiple days. When that happens, even beaches that rarely see contamination — like Wailea and Ko Olina — can have elevated bacteria levels. Runoff can persist after a storm. There is no fixed number of days that clears an active advisory.
The specific bacteria the DOH tests for is enterococci — fecal indicator bacteria found in the intestines of humans and animals. After rain, enterococci enters the ocean through two main pathways: sewage overflow from Hawaii’s approximately 88,000 cesspools, and animal waste washed off agricultural land, urban areas, and forested watersheds. Enterococci can cause gastrointestinal illness, skin infections, ear infections, and eye infections. Children, elderly visitors, and anyone with open wounds are at highest risk.
Hawaii has roughly 88,000 cesspools — more than any other U.S. state. These are unlined underground pits that receive raw sewage and let it seep into the ground and groundwater. During heavy rain, the water table rises and cesspools overflow, pushing untreated human waste directly into streams and coastal waters. The state legislature passed Act 125 in 2017 requiring all cesspools to be converted or replaced by 2050, but progress has been slow. Until then, every heavy rain event is a sewage event.
Routine bacteria samples cannot measure every runoff pollutant or every beach. The September 2024 Hawaii DOH program document lists about 407 BEACH Act beaches statewide and reports that about 167 were monitored in 2023; monitoring frequency varies. Safe to Swim Hawaii shows current official notices separately from historical context. Historical ratings do not replace a missing current measurement.
Use the DOH heavy-rain precaution together with current notices. Elapsed time does not end an active advisory, and clear-looking water does not establish water quality. Stay out of affected water and choose land-based plans when conditions remain uncertain.
People who live in Hawaii and swim year-round don’t just follow a blanket rule. They make decisions based on specific conditions. Here’s the decision-making process most experienced ocean swimmers use.
Rain in the mountains above a beach matters more than rain at the beach itself. The watershed is what feeds the streams. It can be sunny at Waikiki while it’s pouring in the Ko’olau mountains behind it — and that mountain rain will flush right down the Ala Wai Canal to the beach hours later.
Brown or murky water, visible runoff and debris are reasons to stay out even without a posted notice. Clear-looking water does not establish water quality or end an active advisory. Check the current DOH notice for the exact beach.
Use these links to check current notices and dated source information for a possible destination. They are not recommendations to enter the water after rain. Stay out of affected water while an advisory is active.
A Kona low can affect normally dry coasts as well as windward beaches. Check current DOH notices and local conditions; adding days to a wait estimate or seeing clear water does not establish recovery.
Ocean runoff risk is a good moment to choose land-based plans. These Oʻahu options keep the revenue path useful without nudging readers back into affected water.
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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 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. 🤙