The Ala Wai Canal, cesspool legacy, best spots for cleaner water, and when to avoid swimming at Hawaiʻi's most famous beach.
Waikīkī Beach hosts over 4 million visitors per year, making it one of the most visited beaches in the world. What most visitors don't realize is that the water quality here is significantly influenced by the Ala Wai Canal — an artificial waterway that collects urban runoff from a watershed containing thousands of cesspools.
Under normal dry conditions, Waikīkī water quality is generally acceptable. But after rain, the picture changes dramatically. Understanding where and when to swim at Waikīkī can make a big difference for your health.
Before the 1920s, Waikīkī was a network of wetlands, taro fields, fishponds, and rice paddies. The Ala Wai Canal was constructed between 1921 and 1928 to drain these wetlands and make the area suitable for development. The canal diverted three streams (Mānoa, Pālolo, and Makiki) that once flowed through Waikīkī.
Today, the 1.5-mile canal collects urban stormwater runoff from approximately 16 square miles of watershed. This watershed includes dense residential neighborhoods, many of which still rely on cesspools. The canal empties into the ocean at its western end, near the Hilton Hawaiian Village and Ala Wai Yacht Harbor.
The neighborhoods draining into the Ala Wai watershed — Mānoa, Pālolo, McCully, Mōʻiliʻili — contain thousands of cesspools that release untreated sewage into the ground. This contaminated groundwater enters the canal and eventually the ocean. Combined with aging sewer infrastructure that is prone to overflows during heavy rain, the Ala Wai Canal carries a significant pollution load.
The sections of Waikīkī closest to Diamond Head — including Sans Souci Beach (Kaimana Beach) and the area near the Natatorium — are furthest from the Ala Wai Canal outlet and generally have the cleanest water. The Waikīkī Aquarium area and Queen's Surf Beach also tend to test better.
The central stretch near the Royal Hawaiian, Kuhio Beach, and the Waikīkī Wall is moderately influenced by both Ala Wai discharge and ocean flushing. Conditions are usually acceptable in dry weather but can deteriorate after rain.
The area near the Hilton Hawaiian Village, Ala Wai Yacht Harbor, and Duke Kahanamoku Beach is closest to where the Ala Wai Canal empties into the ocean. This section has the most direct exposure to canal discharge and generally has the worst water quality, especially after rain.
After heavy rain, the Ala Wai Canal floods with contaminated runoff from its 16-square-mile watershed. This discharge reaches Waikīkī Beach within hours. Bacteria levels can spike 10-100x above safe limits. Wait at least 72 hours after significant rain and until the water looks clear before swimming, especially at the western (Hilton) end of the beach.
Free alerts when water quality changes at Waikīkī and other Oʻahu beaches.
No spam. Just safety alerts for your trip.
⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent passion project. Information is based on publicly available data, not real-time measurements.
Always verify conditions with the Hawaii DOH Clean Water Branch.
When in doubt, don't go out. 🤙