Oʻahu has the most beaches and the most monitoring — but also the most urban pollution. Maui’s resort coasts are among the cleanest in the state.
Maui’s top resort beaches (Wailea, Kapalua) have better water quality than Oʻahu’s most popular beaches (Waikiki, Ala Moana). However, Oʻahu’s Ko Olina lagoons rival Maui’s cleanest areas, and the North Shore/Windward Coast beaches (Kailua, Lanikai) also rate well.
The main difference is urban impact: Oʻahu has nearly 1 million residents concentrated in Honolulu, with the Ala Wai Canal and urban stormwater systems draining into the same waters tourists swim in. Maui’s resort areas are less densely developed and drier.
Ko Olina’s four engineered lagoons on Oʻahu’s dry west side are the cleanest resort beaches on the island. The UH Water Resources Research Center found 88% of 128 samples had zero detectable enterococci in a 2019 year-long study. No streams, no canal, no urban drainage. Rates 1/5 on our bacteria risk scale.
Kailua Beach and Lanikai rate 1–2/5, with generally excellent water quality. Some concern near Kawainui Marsh drainage at the south end of Kailua Beach after heavy rain, and Enchanted Lake Canal outflow. The trade winds and open ocean exposure help flush the coastline.
Waikiki rates 2/5 with the Ala Wai Canal as the primary concern. Ala Moana Beach Park rates 2–3/5, closer to urban Honolulu and the canal outflow. Both beaches are fine during dry weather but risk elevates significantly after rain. These are Oʻahu’s most visited beaches and also the most affected by urban infrastructure.
North Shore beaches generally have excellent water quality during summer. The rural North Shore has minimal urban development and few pollution sources. However, these beaches are only safe for swimming from May through September due to dangerous winter surf. Haleiwa Beach near the harbor has slightly more runoff risk.
Wailea’s resort beaches are among the cleanest in all of Hawaiʻi. The dry south Maui climate, minimal stream discharge, and well-maintained resort infrastructure keep bacteria levels consistently low. Grand Wailea, Four Seasons, and Fairmont Kea Lani all front excellent beaches. Rates 1/5.
Kapalua Bay is sheltered and clean (1/5). Kaʻanapali Beach rates 1–2/5 — excellent during dry weather but with some stream mouth exposure on the northern end. The 2023 Lāhainā wildfire raised ongoing watershed concerns for the west Maui coast, though beach water quality has largely recovered at most monitoring sites.
• Kahului Bay: Harbor area with commercial shipping and urban runoff. Avoid swimming near the harbor.
• Lāhainā injection wells: Treated wastewater injected underground seeps into nearshore waters. A well-documented EPA concern.
• West Maui streams: After heavy rain, stream mouths between Kaʻanapali and Lāhainā carry sediment and elevated bacteria.
Despite these concerns, Maui’s overall water quality profile is better than Oʻahu’s because the resort areas are less urbanized and the population is roughly one-tenth of Honolulu’s.
Maui’s Wailea coast and Oʻahu’s Ko Olina are equally clean. The difference is in the “default” tourist beaches: Waikiki (Oʻahu) has moderate risk, while Kaʻanapali (Maui) has low risk. If you’re staying at a typical resort, Maui’s beaches will generally have better water quality.
Oʻahu has more DOH Tier 1 monitored beaches and Surfrider supplemental testing than any other island. This means problems are detected faster and advisories are posted sooner. Maui has fewer monitored sites, so some beaches may have issues that go undetected longer.
• Avoid swimming for 72 hours after heavy rain on either island. See our rain safety guide →
• On Oʻahu, avoid the Ala Wai Canal area and swim in central Waikiki or at Ko Olina/Kailua instead.
• On Maui, avoid stream mouths on the west side after rain and stay away from Kahului Bay.
• Check for active advisories at the DOH Clean Water Branch.
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Hawaii DOH Clean Water Branch — Tier 1 beach monitoring, advisories. eha-cloud.doh.hawaii.gov
UH Water Resources Research Center — Ko Olina lagoon study (SR-2020-04), 128 samples, 2019. wrrc.hawaii.edu
Surfrider Oʻahu — BWTF 2024 Report, 26 sites bi-weekly. oahu.surfrider.org
EPA — Lāhainā injection well studies; Maui wastewater discharge research.
⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent passion project — not affiliated with any government agency or monitoring organization. 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 Hawaiʻi’s beaches, and some areas have no regular testing at all.
Always verify current conditions with the Hawaii DOH Clean Water Branch before entering the water.
When in doubt, don’t go out.