The Ala Wai Canal is the single biggest threat to Waikiki water quality. Built in the 1920s to drain wetlands, it now funnels sewage from thousands of cesspools, urban runoff from three major streams, and storm drain overflow directly into the ocean at the western end of Waikiki.
A
2026 study published in Nature Scientific Reports found that 100% of Waikiki’s storm drainage outfalls will fail by 2050 due to rising sea levels and groundwater changes — meaning the problem will get significantly worse.
Bottom line: After heavy rain, bacteria levels near the canal outlet can spike to
many times above safe swimming standards. The western end of Waikiki (near Hilton Hawaiian Village) is most affected. The eastern end near
Kaimana Beach is generally cleaner.
Ala Wai Canal — By the Numbers
88,000
Cesspools statewide (thousands in Ala Wai watershed)
3
Major streams feeding the canal (Mānoa, Pālolo, Mākiki)
100%
Storm outfalls projected to fail by 2050 (Nature, 2026)
$345M+
Proposed Army Corps flood mitigation project cost
How the Ala Wai Affects Waikiki Beaches
During Dry Weather
When it hasn’t rained, the canal flows slowly and most contamination stays within the canal itself. Waikiki beach water quality is generally acceptable during dry periods, though bacteria levels near the canal outlet (Duke Kahanamoku Beach area) tend to be higher than the eastern end of Waikiki.
Lower risk in dry weather
During & After Rain
Heavy rain overwhelms the canal system. Streams carry sewage, animal waste, and urban pollutants into the canal, which overflows into the ocean. A contamination plume spreads along the Waikiki shoreline, elevating bacteria levels well above safe swimming standards. The effect can persist for 72 hours or more after rain stops.
Western Waikiki (Hilton area) — Highest risk
Central Waikiki (Royal Hawaiian area) — Moderate risk
Contamination plume reaches this area during heavy events. Risk drops within 48 hours.
Farthest from canal discharge. Generally cleanest section of Waikiki, even after rain.
High risk after rain
What the Science Says — 2026 Nature Study
100% of Waikiki Storm Drains Will Fail by 2050
A peer-reviewed study published in Nature Scientific Reports (2026) modeled compound flooding in the Waikiki area under sea level rise scenarios. The key findings:
All storm drainage outfalls fail
Rising groundwater and sea levels will render the entire Waikiki drainage system non-functional. Even moderate rain events will cause flooding.
Compound flooding increases contamination
Simultaneous high tides, rain events, and elevated groundwater create worst-case scenarios where the canal cannot drain and overflows into streets and the ocean.
Cesspool conversion may not be enough
Hawaii plans to convert all cesspools by 2050, but rising groundwater may compromise even new septic systems and sewer connections in low-lying areas.
Source: Nature Scientific Reports, 2026. DOI: 10.1038/s41598-026-38225-z
Why This Matters for Swimmers
Approximately 100,000 tourists swim at Waikiki beaches on any given day. Most have no idea that a heavily contaminated canal discharges into the ocean just upstream. The water can look perfectly clear even when bacteria levels are elevated — you cannot see, smell, or taste the contamination.
History of the Ala Wai Canal
1920s — Canal built to drain Waikiki wetlands
Waikiki was originally marshland with taro patches and fishponds. The canal was dredged to drain the area for hotel and resort development. Three streams (Mānoa, Pālolo, Mākiki) were diverted into it.
1960s-1990s — Urbanization increases pollution
As Honolulu grew, storm drains, cesspool seepage, and increased impervious surfaces sent more and more contaminated runoff into the canal. Sediment accumulated, reducing the canal’s capacity.
2006 — Fatal bacterial infection
A canoe paddler died after contracting a flesh-eating bacterial infection from the canal water, drawing national attention to the contamination problem.
2017 — Hawaii cesspool conversion law
Act 125 mandates all 88,000 cesspools statewide be upgraded to septic or sewer by 2050. Implementation is slow and faces funding challenges.
2026 — Nature study reveals 100% drainage failure
Peer-reviewed research shows all Waikiki storm outfalls will fail due to compound flooding, sea level rise, and groundwater changes.
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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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