Toxic bacteria found in Zion waterways: The National Park Service is warning hikers

By Claire Wolters | Fact-checked by Davi Sherman
Published August 10, 2023

Key Takeaways

  • Some Zion National Park waterways contain toxic bacteria that can cause skin and systemic symptoms. 

  • People can be exposed to the bacteria by touching or submerging themselves in water.

  • The National Park Service recommends against swimming in impacted waterways due to exposure risks.

The National Park Service recently detected toxic bacteria in several waterways at Zion National Park. The agency is now issuing warnings and health watch advisories in some areas.[] 

The bacteria found is called cyanobacteria, colloquially known as blue-green algae. It can grow on surfaces like rocks, sticks, and sand and is yellow-brown and “vein textured,” according to the National Park Service. In small amounts, cyanobacteria can be harmless. Large blooms, however, produce cyanotoxins, exposure to which can irritate the skin, eyes, ears, nose, or throat, as well as headaches, vomiting, diarrhea, or seizures.[] 

Dr. Charles Bailey, MD, the Medical Director for Infection Prevention at Providence Mission Hospital and Providence St. Joseph Hospital in Orange County, CA, says that a person’s reaction may depend on the concentration of algae to which they are exposed, the length of exposure, and whether they have any skin conditions, like dermatitis or open sores.

“If you had a group of people that jumped in the same water and came out, I wouldn't expect all of them to have the same symptoms, to the same degree,” Dr. Bailey says. “It would depend on what part of the water they were in, how long they were in it, their general health, and how they tend to manifest the results of an exposure.”

People can be exposed to cyanobacteria through skin contact, including swimming in contaminated water, wearing wet clothing dipped in contaminated water, or drinking the water. It is not airborne and cannot be spread from person to person.[]

Because cyanobacteria is a toxin-producing bacteria and not an infectious disease, people with more robust immune systems are not necessarily safe from exposure. However, some individuals may be able to recover from symptoms more quickly, Dr. Bailey notes. 

In some aspects, cyanobacteria exposure can be compared to poison ivy exposure or “taking a dip in a pool of ‘poison ivy tea.’” The extent of a reaction depends on “how long it's steeped and how long you stay [in],” Dr. Bailey says. 

He adds that there is no specific treatment for cyanobacteria exposure, meaning people may need to simply wait out their symptoms. Those who have not been exposed to the bacteria can protect themselves by avoiding contact with waterways that have been infected, such as the ones at Zion National Park.

The National Park Service urges hikers to take safety precautions but is not closing off trails. Dr. Bailey suggests that people be vigilant about avoiding water exposure but not avoid trails altogether out of fear.[]

When evaluating patients with rashes, doctors should ask about recent travel, hiking trips, or other outdoor activities to determine whether a patient may have been exposed to this bacteria, Dr. Bailey says.

“Obviously, it's a very localized situation,” he adds, “but doctors who are evaluating a rash, especially in a person who's had a history of travel, might [want to] delve a little more deeply into exactly what type of activities they engaged in while they were away from the local area.”

At Zion National Park, health watch advisories have been issued for the following  areas in the North Fork of the Virgin River and La Verkin Creek waterways:[]

  • The Narrows

  • Pine Creek

  • Deep Creek

  • Kolob Creek

  • Orderville Canyon

  • Emerald Pools

  • All canyoneering routes with an active surface water connection to the North Forth of the Virgin River

  • La Verkin Creek

  • Timber Creek

  • Hop Valley Creek

  • All canyoneering routes with an active surface water connection to La Verkin Creek

Warnings have been issued for the following areas of the North Creek waterway:

  • Right Fork

  • Left Fork (The Subway)

  • Grapevine Spring

  • All canyoneering routes with an active surface water connection to North Creek

Warning alerts are slightly more severe than health watch alerts; both are less severe than danger alerts. In warnings or health alerts, the National Park Service recommends that people not swim in or submerge their heads under affected waterways.[]

What this means for you

A toxic bacteria that can cause skin irritation and other symptoms was located in many waterways at Zion National Park. If patients experience new rashes, it may be a good idea to ask them about any recent trips, outdoor swimming, or hiking activities.

Share with emailShare to FacebookShare to LinkedInShare to Twitter