Water quality status and bacteria risk rating
Also known as: Snorkel Beach Kona, Kahaluu Bay
📍 On the Kona coast, about 5 miles south of downtown Kailua-Kona
Kahaluʻu Beach Park is the most popular snorkeling spot on the Big Island, drawing roughly 400,000 visitors per year to its sheltered bay. But the same features that make it beginner-friendly — the ancient rock wall breakwater, shallow warm water, calm conditions — also limit ocean circulation, which means when contaminants enter the bay, they stay longer than at open-ocean beaches.
The bay has a pattern of periodic bacteria exceedances. In January 2026, enterococci levels hit 2,005 per 100 mL — more than 15 times the safe threshold. Similar spikes were recorded in 2019 (324/100mL), 2023 (306/100mL), and August 2025 (164/100mL). DOH consistently says these may not reflect typical conditions, but the pattern is hard to ignore.
UH Hilo marine scientists confirmed the root cause: dye tracer tests proved that cesspool wastewater from nearby homes reaches the shoreline. Stormwater runoff from roads and the parking area also drains into the bay. The Kohala Center, which operates the ReefTeach volunteer program at Kahaluʻu, acknowledges that cesspools and runoff significantly impair water quality.
Based on: DOH Tier 1 weekly monitoring, recurring bacteria exceedances (2019, 2023, 2025, 2026), UH Hilo dye tracer study, sheltered bay with limited flushing, Hawaiʻi Wai Ola community monitoring (5 sites in bay)
Safe threshold: 130 enterococci per 100 mL
UH Hilo Dye Study: Marine scientists added fluorescein dye to a residential cesspool near Kahaluʻu Bay. The dye emerged at a shoreline spring, confirming that wastewater flows directly from homes into the bay. The research team, led by Professor Steve Colbert, is studying sewage pollution hotspots along the Kailua-Kona to Keauhou coastline and how sea level rise will worsen the problem.
Hawaiʻi Wai Ola: This community science program monitors 5 sites within Kahaluʻu Bay, testing for enterococcus, nutrients, turbidity, and other water quality indicators. Their data provides a more complete picture than DOH’s single weekly sample.
Cesspool Priority: Homes in the Kahaluʻu area are designated priority 2 for cesspool replacement under Hawaiʻi’s statewide conversion program (Act 125, 2017). The community and researchers are pushing to raise this priority based on the dye study evidence. All cesspools statewide must be replaced by 2050, but progress has been slow.
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 Kahaluʻu, this is especially important because the sheltered bay doesn’t flush as quickly as open-ocean beaches. Runoff from roads, parking areas, and cesspools concentrates in the bay after storms. The Kona Coast is generally drier than the windward side, but when it does rain, Kahaluʻu is more vulnerable than nearby open-coast beaches.
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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 is for informational purposes only and should not be the sole basis for any swimming decisions.
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