The Hawaii Department of Health tells everyone not to swim or wade in any freshwater stream or pond in Hawaii, and to be especially careful with open cuts or sores. That is health guidance about leptospirosis, a bacterial infection carried in animal urine. That advice applies even when the water looks clean.

Permission to enter an area does not establish safe water quality or protection from flash floods. HawaiiGuide's position is to plan the day around viewing from the built trail or overlook, and to choose a maintained pool when available if swimming is the goal.

Leptospirosis bacteria enter through broken skin or the soft tissue of the mouth, nose, and eyes, and the Department of Health says putting your head under water raises the risk. Wading counts as exposure. So does rinsing your face at a stream crossing.

The bacteria survive in fresh water and wet soil for weeks to months, and the CDC says risk rises after hurricanes, floods, and heavy rain because runoff carries animal urine into streams. Clear water is not evidence the bacteria are absent, and a dry morning does not reset a stream. Choose a walk that avoids stream crossings if you have open wounds. Waterproof bandages are a CDC precaution for exposure; they do not make a natural pool safe to swim in.

Flash floods are the other reason land managers keep people out of gorges. Haleakalā National Park warns that flash floods and sudden rockfalls can occur at any time in the Kīpahulu streams and recommends against entering or wading in them. The National Weather Service explains that flooding can occur away from where the heavy rain fell. Rain upstream can raise the water even when it is not raining where you stand.

If water begins to rise or carries muddy runoff and debris, leave the streambed immediately and move to higher ground. The absence of those signs does not prove the stream is safe. The state's Kalalau Trail safety page says never cross a flooded stream. Keep out of the water while you wait for help or guidance. A drop in water level does not establish that a crossing is safe. The National Weather Service adds that moving water can knock a person down at shallow depths and hides debris. If you are cut off, do not try to cross back. Move to the highest point you can reach and call 911 if you have a signal. DLNR warns that the Nāpali Coast has no cellular coverage. Tell someone your route and return time before you go.

Permission varies by site, and nothing below is a promise a site is open on your date. ʻAkaka Falls State Park has a designated paved route to waterfall viewpoints. Treat it as a viewing visit and check current notices for any trail restrictions before you drive up. At Mānoa Falls, DLNR’s 2018 notice prohibited any entry into the pool area and documented rockfall injuries at the viewing area. That historical notice does not establish today’s trail status. Our recommendation is to stay out of the pool and follow current barriers and trail notices.

The Pools of ʻOheʻo in Haleakalā National Park are not open for entry and can be viewed from the Kūloa Point Trail. Sacred Falls State Park on Oʻahu has been closed since a fatal 1999 rockfall, and the state cites people found inside. Check current access before choosing a trail. The state publishes closure and access updates on its park notices page. Follow those notices and all posted barriers; an older trail description does not establish today's access.

Our recommendation is to skip jumping, diving and rope swings into natural waterfall pools. Our recommendation applies even if other visitors are already in the water. Haleakalā National Park lists jumping and diving hazards alongside slippery rocks, rockfall and water-quality risks. Swimming to inspect a pool still means entering the freshwater that the Department of Health advises avoiding. Our recommendation is to stay out, including for a bottom inspection.

Keep out of the closed Pools of ʻOheʻo. At Mānoa and other waterfalls, follow the land manager's boundaries and the state's advice to avoid the base of waterfalls and steep cliffs. View from the designated route instead of stepping beneath a falling-water or rockfall zone.

HawaiiGuide's recommendation is to make the viewpoint the goal, not the swim. Pick a falls with a designated trail or overlook from our waterfall guide, confirm the land manager's status the morning you go, and check Travel Alerts and current conditions alongside the NWS Honolulu forecast and alerts. If a flood watch or warning affects your planned area, choose a different activity. Our pages on ʻOheʻo Gulch and the Mānoa Falls Trail help you plan a viewing visit; current official notices still govern access.

Build in a weather-dependent fallback. If heavy rain is forecast in the mountains, the gorge is the wrong place to be. Move the walk to another day. If you want to swim, choose a maintained pool when available and confirm access. If you choose the ocean, use our beach warning signs and lifeguard guide and ask an on-duty lifeguard about conditions. Ocean swimming has its own hazards. Save your viewing stop and fallback in My Trip so the decision is easy on the day.

Symptoms can begin anywhere from 2 to 30 days after exposure and look like a common flu: fever, headache, muscle aches, chills, red eyes, nausea. Some people feel better and then get sick again. Without treatment the infection can damage the kidneys or liver, cause meningitis, or lead to breathing failure. If you develop these symptoms within 30 days of freshwater contact in Hawaii, seek medical care right away and say where you were in the water. CDC guidance tells clinicians to start antibiotics promptly when they strongly suspect leptospirosis, without waiting for test results, so mentioning the exposure matters. A clinician should decide testing and treatment. Do not self-prescribe antibiotics.