Water quality status and bacteria risk rating
Also known as: Princeville Beach
📍 On Kauaʻi's north shore, below the Princeville resort community
Hanalei Bay has been listed as impaired for enterococcus bacteria by the Hawaii DOH since 2004. Four streams and rivers discharge into the bay: the Hanalei River, Wai'oli Stream, Waipa Stream, and Waikoko Stream. The Hanalei River watershed originates at Mount Wai'ale'ale, which receives over 400 inches of rainfall per year, flushing sediment and bacteria into the bay.
Over 360 active cesspools exist between Hanalei and Ha'ena, leaching untreated human waste into groundwater. Stanford University and USGS research confirmed human wastewater markers in the bay's waters. The EPA has established a Total Maximum Daily Load (TMDL) for bacteria, sediment, and nutrients in the bay.
Risk varies dramatically by location. Near the river mouth at Black Pot Beach/Pier, bacteria is chronically elevated. The outer western parts of the bay have substantially better water quality due to greater ocean flushing.
Based on: DOH impaired waters listing (2004–present), Surfrider Kauai BWTF 2024, EPA Hanalei Bay TMDL, Hanalei Initiative cesspool mapping, Stanford/USGS source tracking
Kauai's North Shore is one of the wettest places on Earth. After any significant rainfall, the Hanalei River turns brown and flushes contaminated runoff directly into the bay. If you can see discolored water entering from the river at the east end of the bay, bacteria levels are almost certainly elevated — even in parts of the bay that look clear. Wait at least 72 hours after rain stops and look for clear conditions before swimming, particularly near the pier area.
Cesspools are simple holes in the ground that collect household wastewater without treating it. Unlike septic systems, they do not filter or break down waste. The untreated sewage seeps into groundwater, which flows into streams and the ocean.
Kauai has approximately 14,000 cesspools island-wide, with over 360 concentrated in the Hanalei to Ha'ena corridor. Hawaii passed Act 125 in 2017 requiring all cesspools to be upgraded by 2050, but progress has been slow. The Hanalei Initiative has been mapping and prioritizing the highest-risk cesspools and working with homeowners to upgrade their systems, but many remain active.
If you're set on swimming at Hanalei, position matters. Avoid the east end near the pier and river mouth (Black Pot Beach) — this is where bacteria is worst. The western sections of the bay have more ocean circulation and less direct river influence. Watch the river mouth when you arrive: if the water is brown or murky where it enters the bay, conditions are poor throughout.
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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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