Water quality data for Hawaii's largest sheltered bay — bacteria risk rating, cesspool contamination, and live DOH advisories
📍 On Oʻahu's windward coast, north of Kailua
"Kane'ohe" Bay water quality today: This bay carries a high 4/5 historical bacteria risk (Grade D — Poor). Surfrider Foundation documented 77%+ bacteria failure rates at testing sites in the bay. Multiple streams carry cesspool-contaminated runoff into the bay, and its enclosed shape traps pollutants rather than flushing them to open ocean. After rain: conditions may be particularly concerning — DOH recommends waiting at least 72 hours. The bay is popular for sandbar tours and kayaking, but bacteria levels have been consistently elevated in testing. Check live advisory status above and make your own judgment.
"Kane'ohe" Bay is famous for its sandbar (Ahu o Laka) and kayaking. These tours operate in the bay — check current water quality advisories before booking.
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The largest sheltered body of water in Hawaii, stretching 7 miles along Oʻahu's windward coast. The bay is famous for the Kaneʻohe Sandbar (Ahu o Laka) — a shallow area in the middle of the bay that emerges at low tide and is one of Oʻahu's most popular boat tour destinations. Coconut Island (Moku o Loʻe), home to the Hawaii Institute of Marine Biology, sits within the bay. Multiple streams drain into the bay from the Koʻolau Mountains, carrying runoff from residential areas with aging cesspools.
"Kane'ohe" Bay has chronic, well-documented water quality problems. Surfrider Foundation's Beach Water Testing & Forecasting (BWTF) program found 77%+ bacteria failure rates at testing sites within the bay. The bay is Hawaii's largest sheltered bay, and its enclosed shape — protected by a barrier reef — means pollutants accumulate rather than flushing to open ocean.
Multiple streams carry contaminated runoff into the bay: "Kane'ohe" Stream, "He'eia" Stream, Waikane Stream, and Waiahole Stream. The "Kane'ohe" watershed is designated a Priority 2 cesspool area by the state, meaning aging cesspools leach untreated sewage into groundwater and streams that feed the bay.
Based on: Surfrider BWTF 2024 (77%+ failure rate), Priority 2 cesspool area designation
"Kane'ohe" Bay stretches approximately 8 miles along the windward coast. Water quality varies by location, but the enclosed nature of the bay means contamination affects all areas to some degree.
"Kane'ohe" Stream and other waterways empty into the southern part of the bay. This area receives the most direct cesspool-contaminated runoff and has the highest bacteria concentrations, especially after rain. Shoreline areas near stream mouths are the most affected.
The famous sandbar sits in the middle of the bay. While farther from direct stream outlets, it is still within the enclosed bay where pollutants accumulate. After rain, bacteria levels at the sandbar can be elevated. The sandbar is a major tourist attraction with heavy boat traffic.
Marine Corps Base Hawaii occupies the eastern edge of the bay. The base has its own wastewater treatment and stormwater systems. DOH advisories sometimes reference MCBH or Mokapu specifically. This area also receives bay-wide pollutant circulation.
Home to the Hawaii Institute of Marine Biology. Located in the bay's interior, subject to the same enclosed-bay water quality conditions. Researchers here study the bay's ecology and pollution impacts.
The Cesspool Problem: "Kane'ohe" is designated a Priority 2 cesspool area. Hawaii has approximately 88,000 cesspools — the most of any state — and the "Kane'ohe" watershed has a high concentration of these aging systems. Cesspools discharge untreated sewage directly into the ground, where it seeps into streams and groundwater that feed the bay.
The Enclosed Bay: Unlike open-coast beaches where ocean currents flush pollutants, "Kane'ohe" Bay is protected by a barrier reef. This means contaminants that enter the bay tend to stay there, accumulating over time. The bay's slow water exchange rate is a key factor in the persistently high bacteria levels documented by Surfrider.
Multiple Stream Inputs: At least four major streams — "Kane'ohe" Stream, "He'eia" Stream, Waikane Stream, and Waiahole Stream — carry runoff from residential and agricultural areas into the bay. Each stream drains neighborhoods with cesspools and urban infrastructure, delivering bacteria, sediment, and nutrients.
Military Presence: Marine Corps Base Hawaii (MCBH) on the Mokapu Peninsula has its own wastewater treatment facility. The base's stormwater runoff and treated discharge enter the bay. DOH has issued advisories specific to MCBH waters in the past.
Less rainfall means less runoff, but "Kane'ohe" Bay's enclosed shape means even dry-season bacteria levels are elevated compared to open-coast beaches. Surfrider's failure rates reflect year-round conditions, not just wet season.
Heavy rain dramatically worsens conditions. All four major streams spike with cesspool-contaminated runoff. The bay turns brown. Windward Oʻahu receives the heaviest rainfall on the island. Conditions may be particularly concerning for extended periods after storms.
"Kane'ohe" receives approximately 60 inches of rain annually, with the Koʻolau mountains above the bay receiving 200+ inches.
The Hawaii Department of Health recommends staying out of the ocean for at least 72 hours after heavy rain, even if the water looks clear. At "Kane'ohe" Bay, this is especially important because multiple streams carry cesspool-contaminated runoff into an enclosed bay that does not flush efficiently. Given the bay's 77%+ bacteria failure rate in Surfrider testing, conditions may be concerning even in dry weather. After rain, the risk increases substantially.
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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.
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