How long should you wait to swim after rain in Hawaii?

The 72-hour rule, explained simply

Hawaii’s Department of Health recommends waiting at least 72 hours after heavy rain before ocean swimming. The reason: rain washes pollutants — animal waste, soil, urban runoff, and (in cesspool-heavy areas) sewage — through streams and storm drains and into the ocean. Bacteria levels can spike 500% above the EPA threshold within 24 hours of heavy rain.

But 72 hours is a conservative default. The actual recovery time depends on:

• Streams nearby? Wet stream-fed coasts (Hilo, Hanalei, North Shore Oʻahu) take longer because watershed discharge continues for days after rain stops.
• Reef protection? Reef-enclosed beaches like Hanauma Bay or Ko Olina Lagoons exchange water with the open ocean slowly, so contamination dissipates more slowly — but they also receive less from streams in the first place.
• Dry coast or wet coast? The Kohala Coast (Big Island) gets ~10 inches of rain per year and has no streams reaching the resort beaches. South Maui (Wailea) sits in Haleakalā’s rain shadow. Ko Olina is on Oʻahu’s dry leeward side. Poʻipu is in Kauaʻi’s rain shadow. These coasts recover in 24-48 hours.
• Cesspools upstream? Hawaii has 88,000+ cesspools statewide. Heavy rain saturates them and discharges raw sewage into streams. Areas with dense cesspool coverage (Kauaʻi north shore, parts of Big Island Hilo, parts of Oʻahu Windward) take longer to clear.

The picker above uses these factors to give you a more specific answer than “72 hours.”

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