The driest coast in the state. No streams, no cesspools, no development runoff. And then there’s Kona, 20 miles south, with bacteria readings 15x the safe limit.
The Kohala Coast resort corridor has the strongest case for cleanest resort water in all of Hawaii. Hapuna Beach, a DOH Tier 1 monitored beach, consistently tests among the cleanest statewide. The geography is ideal: roughly 10 inches of annual rainfall, zero streams reaching the ocean, no cesspools in the coastal zone, and young lava flows that absorb what little rain falls.
The contrast with Kona — just 20 miles south — is dramatic. Kahalu’u Beach Park recorded 2,005 enterococci per 100mL in January 2026, fifteen times the safe limit, from confirmed cesspool groundwater plumes.
The Kohala Coast stretches from Kawaihae south to Waikoloa along the Big Island’s dry leeward shore. Unlike every other resort area in Hawaii, it has virtually none of the three major pollution sources that affect beach water quality:
No streams. The coast sits on young, porous lava flows from Mauna Kea and Mauna Loa. Rainfall (what little there is) percolates through the rock rather than forming surface streams. There are no rivers, no stream mouths, and no channels carrying runoff to the beach.
No cesspools. The resort properties use modern wastewater treatment. Unlike Kona (14,000+ cesspools) and Hanalei (360+), the Kohala Coast resort zone has no cesspool infrastructure leaching sewage toward the shoreline.
Minimal rainfall. At roughly 10 inches per year near Waikoloa, this is the driest stretch of coastline in the state. Less rain means less of everything that causes water quality problems: less runoff, less erosion, less pollutant transport.
Source: NOAA climate normals; USGS Hawaii stream gauge network; Hawaii DOH cesspool conversion priority areas
The one nuance on the Kohala Coast is the presence of anchialine ponds — brackish pools in porous lava rock that connect to the ocean through underground channels. These are concentrated around A-Bay (Anaehoomalu Bay), behind the Mauna Lani, Fairmont Orchid, and Hilton Waikoloa properties.
Anchialine ponds are ecologically important habitats, home to endemic shrimp species. They can influence nearshore water chemistry through groundwater exchange. This is not the same as stream runoff or cesspool contamination — it’s natural brackish water mixing. But it’s the reason we rate A-Bay area beaches as Low–Moderate rather than the Low given to Hapuna and Kauna’oa Bay, which don’t have this influence.
Source: USGS anchialine pond surveys; UH coastal hydrology studies
The stark contrast with Kona is what makes the Kohala Coast story so compelling. Just 20 miles south of the resorts, Kailua-Kona has an estimated 14,000+ active cesspools — among the highest concentrations in Hawaii.
Kahalu’u Beach Park is the most dramatic example. UH Hilo researchers have confirmed a sewage plume reaching the ocean through groundwater at this popular snorkeling beach. In January 2026, bacteria hit 2,005/100mL — fifteen times the safe limit. This is a chronic, confirmed problem, not a one-time event.
Spencer Beach Park at Kawaihae (between Kohala and Kona) recorded 178/100mL in February 2026 — also above the safe limit. Spencer sits at the southern boundary of the Kohala Coast area and is closer to developed areas with older infrastructure.
If you’re staying on the Kohala Coast and considering a day trip to Kona, check for active advisories at Kona beaches before swimming. The geology that protects the Kohala Coast — porous lava with no streams — is the same geology that lets Kona’s cesspool plumes reach the ocean through groundwater.
Source: DOH CWB advisory (Jan 2026); UH Hilo cesspool groundwater studies; Hawaii County cesspool conversion program; Big Island Now (Feb 2026)
The Kohala Coast is the safest bet in Hawaii. Hapuna Beach and Kauna’oa Bay (Mauna Kea Beach Hotel) are the standouts. You’re swimming in open ocean on the driest coast in the state with zero pollution sources.
Kona has amazing snorkeling (when clean) and cultural sites. But check the DOH advisory page before swimming at any Kona beach, especially Kahalu’u. Consider Captain Cook / Kealakekua Bay as an alternative — it’s a protected marine reserve with better water quality than the Kailua-Kona town beaches.
The Kohala Coast is as close to “always clean” as Hawaii gets, but universal rules still apply: avoid swimming after heavy rain (rare but it happens), don’t enter murky water, and rinse off after ocean swimming. Full rain safety guide →
Hawaii DOH Clean Water Branch — Beach monitoring, advisories. eha-cloud.doh.hawaii.gov
UH Hilo — Cesspool groundwater plume studies, Kahalu’u Beach. hilo.hawaii.edu
NOAA / NWS — Climate normals, rainfall data.
Big Island Now — DOH advisory reporting (Kahalu’u Jan 2026; Spencer Feb 2026).
⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent passion project — not affiliated with any government agency. Assessments are based on publicly available data. They are not real-time measurements. “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 with the Hawaii DOH Clean Water Branch before entering the water.
When in doubt, don’t go out. 🤙