Bacteria data, DOH advisory status, and water quality history for one of the Big Island's most iconic beaches
📍 Also known as Kaunoa Beach · at the Mauna Kea Beach Hotel (Autograph Collection)
Mauna Kea Beach water quality: This beach carries a low 1/5 historical bacteria risk — protected on the dry Kohala Coast with no stream inputs. However, it has recorded bacteria exceedances that are unusual for this type of beach: 238 Enterococcus/100mL in June 2023 and 178/100mL in February 2026, both above the 130/100mL DOH threshold. The source of these periodic spikes is unclear since there are no obvious runoff inputs. DOH Tier 1 monitored. Check live advisory status above and make your own judgment.
The Kohala Coast is a hub for snorkeling, sunset cruises, and cultural tours. When conditions are clear, the water along this coast is some of the best in Hawaii.
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Mauna Kea Beach (Kaunoa Beach) is a DOH Tier 1 monitored beach on the dry Kohala Coast. With no stream inputs and minimal rainfall (~10 inches/year), conditions are typically excellent. The crescent-shaped, white sand beach is protected by a reef that keeps the water calm most of the year.
However, periodic bacteria exceedances have been documented despite the favorable conditions: 238 Enterococcus/100mL in June 2023 and 178/100mL in February 2026, both above the 130/100mL DOH action threshold. These spikes are unusual for a beach with no obvious runoff sources and may be related to groundwater seepage, wildlife, or other non-point sources.
Based on: DOH Tier 1 beach monitoring, Kohala Coast dry climate, documented bacteria exceedances, geographic risk assessment near Puʻukoholā Heiau
Most Kohala Coast beaches have consistently clean testing records. Mauna Kea Beach is an exception — it has recorded bacteria levels above the DOH threshold on multiple occasions, which is unexpected for a dry coast beach with no stream inputs.
Enterococcus measured at 238 per 100mL, nearly double the 130/100mL DOH action threshold. This reading triggered monitoring attention for a beach that typically tests well below limits.
A second documented exceedance at 178/100mL, above the 130/100mL threshold. The recurrence suggests an intermittent contamination source rather than a one-time anomaly. The specific cause has not been publicly identified.
The majority of DOH testing results at Mauna Kea Beach come back well below the 130/100mL threshold. The dry Kohala Coast climate and lack of stream inputs keep baseline conditions clean. The exceedances, while concerning, are the exception rather than the norm.
Bacteria exceedances at Mauna Kea Beach are puzzling because the Kohala Coast lacks the typical contamination sources — no streams, minimal rainfall, no marsh drainage. Several possible explanations exist:
Groundwater seepage: The Big Island's porous lava rock allows groundwater to reach the ocean through submarine springs. If this groundwater carries nutrients or bacteria from inland sources (including the hotel's grounds and golf course), it could affect nearshore water quality periodically.
Wildlife concentration: Mauna Kea Beach is a popular nesting area. Birds and marine life concentrating in the sheltered cove could contribute to periodic bacteria spikes, especially during calm ocean conditions when water circulation is reduced.
Rare rainfall events: When it does rain on the Kohala Coast, stormwater from hotel grounds, parking areas, and the golf course drains toward the shoreline. Because rain is so infrequent, the accumulated material can produce a concentrated pulse of contamination.
Minimal rainfall on the Kohala Coast. Ocean is typically calm with excellent visibility. Trade winds keep conditions pleasant. This is the best time for swimming and snorkeling at Mauna Kea Beach.
Occasional Kona storms can bring rare rainfall to the dry coast. North swells may create larger surf. Both documented bacteria exceedances occurred in different seasons (June and February), so no clear seasonal pattern has emerged.
The Kohala Coast receives approximately 10 inches of rain per year — far less than Hilo (130 in) or the Hamakua Coast (100+ in).
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. Rain is rare on the Kohala Coast, but when it does fall, accumulated material from hotel grounds, golf courses, and parking areas can wash into the nearshore waters. The Big Island's porous lava rock means runoff behavior is different from other islands — water can appear underground and seep through the shoreline.
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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 clean. DOH only monitors a fraction of Hawaii’s beaches, and some areas have no regular testing at all.
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