Trade wind side: wetter, greener, fewer tourists, and some of Hawaiʻi’s best beaches.
The Hawaii Department of Health recommends staying out of the ocean for at least 72 hours after heavy rain. The windward side receives significantly more rain than Waikiki. Kailua Beach’s north end is affected by Kawainui Marsh drainage. Always check conditions after rain.
Windward Oʻahu is the island’s eastern coast, stretching from Makapuʻu Point in the south through Waimanalo, Kailua, Kaneʻohe, and up to Laʻie in the north. The Koʻolau Mountains form a dramatic backdrop, their fluted green cliffs rising directly behind the coastal towns.
The windward coast is primarily residential rather than resort-oriented. Kailua is an upscale beach town with boutique shopping. Kaneʻohe is a working-class community. Waimanalo retains a rural character. There are almost no high-rise hotels on the windward side — most visitors come as day-trippers from Waikiki.
The trade-off for the lush greenery is more rain. Kailua receives about 50 inches per year. This means more frequent stormwater-driven bacteria events compared to the south shore. Understanding which parts of the coast are most and least affected by runoff is key.
The windward coast of Oʻahu faces the northeast trade winds. The Koʻolau Mountains wring moisture from these winds, creating the lush, green landscape that defines this side of the island. Fewer tourists venture here, but the beaches — Kailua, Lanikai, Waimanalo — are among Hawaiʻi’s finest.
Length: 2.5 miles of white sand
Facilities: Lifeguards, restrooms, showers, kayak rentals, parking
Character: Repeatedly voted best beach in the US. Turquoise water, gentle waves, offshore islands (the Mokes).
Water quality note: The north end near Kawainui Marsh can have elevated bacteria after rain. The marsh drains through a channel into the north end of the beach. The south end (near Lanikai) is generally cleaner.
Access: 11 narrow public access paths between houses. No signs, no parking lot, no restrooms, no lifeguards.
Character: Postcard-perfect. Calm, clear water with the Mokulua Islands offshore. Residential neighborhood — do not park in driveways or on lawns.
Water quality note: Generally cleaner than the north end of Kailua because there is no significant stream or marsh outlet.
Length: 3.5 miles — the longest sandy beach on Oʻahu
Character: Less touristy, more local. Wider beach with fine white sand backed by ironwood trees. Bellows Field Beach (military beach open to the public on weekends) is at the south end.
Water quality note: Generally good due to open-ocean exposure, though stream outlets along the beach can create localized contamination after rain.
Character: Large, shallow bay. Not a swimming destination. Murky water from freshwater input and enclosed shape.
Activities: Kaneohe Sandbar tours (wade on the sandbar at low tide), kayaking, fishing. Heʻeia Fishpond is a restored Hawaiian aquaculture site.
Water quality note: The bay has chronic turbidity and elevated bacteria counts. Multiple streams drain into it. Not recommended for ocean swimming.
Water quality on the windward coast varies more dramatically than any other area of Oʻahu. During dry weather, the open-ocean beaches can have excellent water clarity. After rain, bacteria levels spike due to multiple stream outlets.
Primary contamination sources: Kawainui Marsh (drains into north Kailua Beach), Kaneohe Bay’s multiple streams, cesspools in older residential areas, and agricultural runoff from Waimanalo. The lowest-risk option after rain is Lanikai (no stream outlets) or the south end of Kailua Beach.
The windward side has very limited hotel options — no major resort properties. Most visitors stay at vacation rentals, B&Bs, or come as day-trippers from Waikiki. For a full-service resort, Turtle Bay Resort on the North Shore is 40 minutes north of Kaneʻohe.
From Waikiki: Kailua is about 15 miles, a 25-35 minute drive through the Pali Highway tunnel. Waimanalo is about 20 miles via the scenic coastal route past Hanauma Bay and Makapuʻu Point.
Parking: Kailua Beach Park has a large lot that fills on weekends by mid-morning. Lanikai has virtually no public parking — cars parked illegally are ticketed quickly. Waimanalo has easier parking.
Restrooms: Kailua Beach Park has full facilities. Lanikai has zero public restrooms. Waimanalo Beach Park has restrooms and showers.
Summer months (May through September) offer the best conditions: less rain, calmer seas, and lower bacteria risk. Visit on weekdays if possible — Kailua Beach is heavily used by locals on weekends. Early mornings have the calmest winds and best water clarity, especially at Lanikai.
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Every beach page on this site includes a historical bacteria risk rating from 1 (low) to 5 (high), based on DOH testing data, Surfrider Foundation monitoring, geographic factors like stream proximity and cesspool contamination areas, and historical advisory frequency. These ratings reflect long-term patterns — not current conditions. Always check the live advisory status at the top of each beach page before swimming.
The Hawaii Department of Health monitors approximately 57 beaches statewide through its Tier 1 and Tier 2 testing programs. Many popular beaches have no regular testing. This site aggregates data from DOH, USGS stream monitoring, NOAA ocean conditions, and NWS weather alerts to provide broader coverage.
After heavy rain, streams carry bacteria, sewage, pesticides, and sediment into the ocean. Bacteria levels can be dangerously high even when the water appears clear. The DOH recommends waiting at least 72 hours after heavy rain before swimming, especially near stream mouths and canal outlets.
Beaches on dry, leeward coasts typically recover faster than beaches near major stream outlets. Open ocean beaches with strong wave action flush contamination more quickly than sheltered bays and lagoons.
100+ beaches across all islands
Safe to Swim Hawaii aggregates water quality data from six independent sources to provide broader coverage than any single agency. Our sources include the Hawaii Department of Health Clean Water Branch (beach advisories and bacteria testing), USGS National Water Information System (25 stream monitoring stations across all islands), NOAA CO-OPS (tide levels and water temperature), NDBC (wave buoys and ocean conditions), NWS Honolulu (weather and marine alerts), and City & County of Honolulu Environmental Services (Kailua Bay water testing and spill reports).
Historical bacteria risk ratings on this site are based on DOH testing data, Surfrider Foundation monitoring, geographic analysis (stream proximity, cesspool contamination areas, coastal development), and advisory frequency. These are historical assessments, not live measurements. Always check the live advisory status at the top of each page and verify conditions with the Hawaii DOH Clean Water Branch before entering the water.
Less rainfall means less runoff and generally cleaner ocean water across all islands. Stream flows drop, reducing bacteria transport to coastal areas. This is typically the best time for ocean water quality, though localized contamination from cesspools and urban runoff can still occur.
Frequent heavy rain events cause stream flooding, sewage overflows, and brown water advisories. Windward and north-facing coasts receive more rain. The DOH issues the most advisories during this period. Leeward coasts (west-facing) generally stay drier and cleaner year-round.
Water quality patterns vary significantly by location. Beaches near stream mouths and urban areas show the most dramatic seasonal variation. Open ocean beaches with strong wave action maintain better water quality year-round. Check individual beach pages for location-specific seasonal data.
Hawaii has approximately 88,000 cesspools — more than any other U.S. state. These underground chambers collect untreated household sewage and allow it to leach into the surrounding soil and groundwater. In coastal areas, this contaminated groundwater eventually reaches the ocean through submarine groundwater discharge, contributing to elevated bacteria levels at nearby beaches.
Hawaii Act 125 (2017) requires all cesspools to be upgraded or converted to approved septic systems by 2050. Priority areas near the coast and drinking water sources are being addressed first, but progress has been slow. Beaches in known cesspool contamination zones carry elevated bacteria risk even during dry weather. For more information, see our comprehensive cesspool guide.
⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent passion project — not affiliated with the Hawaii Department of Health or any government agency. Water quality ratings are estimates based on publicly available testing data and geographic analysis. They are not real-time measurements and may not reflect current conditions.
Always verify current water quality conditions with the Hawaii DOH 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. 🤙
Safe to Swim Hawaii checks water quality data every 15 minutes from multiple government agencies. When conditions change — a new advisory is posted, stream levels spike after rain, or an advisory is cancelled — our pages update automatically. This means you are seeing the latest available data from official sources, not a static snapshot.
The Hawaii Department of Health Clean Water Branch operates the state’s official beach monitoring program. Tier 1 beaches are tested weekly; Tier 2 beaches are tested less frequently. When bacteria levels exceed 130 enterococci per 100 mL, the DOH issues a Beach Advisory for that location. Brown Water Advisories are issued based on visual assessment of runoff conditions, not bacteria testing.
USGS stream monitoring stations measure water flow (discharge) and turbidity in real time. When a stream near a beach is flowing at 5x or more above its normal rate, this indicates significant runoff that likely carries elevated bacteria. We display these stream conditions alongside DOH advisories to give a more complete picture of water quality at each beach.