The real health risks of swimming in discolored ocean water in Hawaiʻi — symptoms to watch for, timelines, and when to see a doctor.
This guide is for general informational purposes only and is not a substitute for professional medical advice. If you develop symptoms after swimming, see a doctor or visit an urgent care clinic. Hawaiʻi has excellent medical facilities on all major islands.
When Hawaiʻi gets heavy rain, stormwater washes soil, debris, and contaminants from land into streams and out to the ocean. The brown color comes from suspended sediment — but the sediment itself is not the primary health concern. What makes brown water dangerous is what it carries: bacteria from cesspools and septic systems, animal waste from agricultural land, chemicals from roads and parking lots, and pathogens from sewage system overflows.
Hawaiʻi has approximately 88,000 cesspools — more than any other state. These underground chambers release untreated sewage directly into the groundwater, which flows into streams and the ocean. After rain, this contamination surges. The brown color is essentially a visible warning sign that the water is carrying more than just dirt.
The most common health outcome from swimming in contaminated water. Swallowing even small amounts of water containing Enterococcus or E. coli can cause nausea, vomiting, diarrhea, and abdominal cramps. Children are at higher risk because they tend to swallow more water during play.
Onset: Typically 12–48 hours after exposure
Duration: 1–5 days in most cases
Water trapped in the ear canal after swimming creates a warm, moist environment where bacteria thrive. In contaminated brown water, the bacterial load is significantly higher, increasing infection risk. Symptoms include itching, pain when pulling on the ear, redness, and fluid drainage. Untreated, it can progress to severe pain, swelling, and fever.
Onset: 1–3 days after exposure
Duration: 7–10 days with treatment
Bacteria in brown water can cause skin irritation ranging from mild rashes to serious infections. The risk is significantly higher if you have cuts, scrapes, or abrasions — including minor reef cuts that are extremely common among snorkelers in Hawaiʻi. Staph infections, including MRSA, can enter through broken skin exposed to contaminated water.
Onset: Hours to 2 days after exposure
Watch for: Increasing redness, warmth, swelling, or pus around any wound
Contaminated water splashing into your eyes can cause conjunctivitis (pink eye) or more serious bacterial eye infections. Snorkelers and body surfers are particularly vulnerable because their eyes are frequently exposed to water. Contact lens wearers face additional risk, as bacteria can become trapped between the lens and the eye.
Onset: 1–3 days after exposure
Symptoms: Redness, itching, discharge, light sensitivity
In rare cases, brown water exposure can lead to more serious infections. Leptospirosis is a risk near stream mouths where freshwater mixes with ocean water. Vibrio bacteria, including Vibrio vulnificus, thrive in warm coastal waters and can cause severe wound infections or life-threatening bloodstream infections in people with liver disease, diabetes, or compromised immune systems.
Many people swim in brown water in Hawaiʻi and feel perfectly fine afterward. This does not mean the water was safe. Healthy adults with strong immune systems may be exposed to bacteria without developing symptoms. But their experience does not predict what will happen to you, your children, or elderly family members.
Bacteria levels in post-rain ocean water can be wildly inconsistent. One swimmer may be in a relatively clean pocket of water while another, just 50 feet away, encounters a concentrated plume of contaminated runoff. Water currents, wave action, and proximity to stream mouths all create a patchwork of contamination levels that change by the minute.
The epidemiological data is clear: swimming in water with elevated bacteria levels increases illness rates. A landmark EPA study found that swimmers at beaches with Enterococcus levels above 130 CFU/100mL had significantly higher rates of gastrointestinal illness compared to non-swimmers. Hawaiʻi uses this 130 threshold as its advisory trigger.
The single most effective prevention strategy is simple: do not swim for at least 72 hours after heavy rain. This applies to all beaches in Hawaiʻi, but especially those near stream mouths, canal outlets, and areas with high cesspool density.
Brown water advisory active? Here are top-rated land-based activities across Hawaiʻi.
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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. This page provides general health information and is not medical advice. If you suspect an infection from swimming, consult a healthcare professional.
Always verify current water quality conditions with the Hawaii Department of Health Clean Water Branch before entering the water.
When in doubt, don't go out. 🤙