Toxic Cyanobacteria Bloom in the Virgin River and the Streams of Zion National Park

cyanobacteria growth underwater
Cyanobacteria colonies like this will grow on rocks, sticks, and sand. Note the ribbed texture.


Updated March 23, 2021


Since a reported pet fatality in July 2020, Zion National Park staff have been actively monitoring for the presence of harmful cyanobacteria and cyanotoxins in three major tributaries of the Virgin River within the park: North Fork of the Virgin River, North Creek, and La Verkin Creek. Harmful cyanobacteria have been present in all monitored tributaries through the winter, however, toxin concentrations were low. In the month of March, detected toxin concentrations have increased in the North Fork of the Virgin River to a level that poses a risk to recreators. Therefore, a Danger Advisory has been issued for the North Fork of the Virgin River based on the concentration of cyanotoxins. Visitors are encouraged to avoid all contact with the water until further notice. North Creek has been issued a Warning Advisory based on the presence of cyanotoxins. La Verkin Creek has been issued a Health Watch based on the presence of harmful cyanobacteria which may produce cyanotoxins. Visitors should avoid primary contact (i.e. swimming or submerging your head) with water in North Creek and La Verkin Creek. Visitors should not filter drinking water from any streams in the park until further notice.

How Does This Affect Your Visit?

  • Children are especially vulnerable to cyanotoxins - minimize risk by avoiding contact with water bodies.

  • Do not submerge your head in the water. Toxins can enter the body by swallowing water or through the nose, eyes, or open wounds.

  • Do not drink river water. There is no known recreational water filtration method that is effective at clearing water of cyanotoxin.

  • Some permitted activities, such as technical canyoneering, are allowed. Permits are still required. Check with the Wilderness Office at 435-772-0170 for more information.

You can visit Utah Department of Water Quality ( for the most up to date information and to learn more about cyanobacteria and algal blooms.

More Information About Cyanobacteria

  • Cyanobacteria of the genus Microcoleus, Tychonema, and Nostoc have been found in the North Fork of the Virgin River, North Creek, and La Verkin Creek. Colonies of cyanobacteria can be red, yellow, tan, green, brown, or black in color.

  • Children and dogs are especially susceptible to being exposed to anatoxin-a. Anatoxin-a can be absorbed through the eyes, nose, or mouth by swimming in or submerging accidentally into contaminated water. Symptoms include skin rash, salivation, drowsiness, tingling, burning, numbness, pain, incoherent speech, seizures, vomiting, and diarrhea.

  • Contact the Utah Poison Control Center at (800) 222-1222 with concerns about anatoxin-a poisoning and call 911 in the event of a medical emergency.

  • There is no known recreational water filtration method that is effective at clearing water of cyanotoxins.

  • Dogs must be kept on a leash. If a pet breaks away and gets into the river, remove them from the water immediately, rinse off their fur thoroughly, and monitor for symptoms of toxin poisoning. A dog can die in as little as 15 minutes from anatoxin-a poisoning. More information about the danger to dogs from anatoxin-a.

More information on cyanobacteria and its health risks to humans can be found at these links:

  • EPA

  • Utah Department of Health

  • Some cyanobacteria produce dangerous nervous system toxins. When in abundance, toxin concentrations can elevate to levels that affect the health of organisms exposed to them, including people, pets, and livestock. Humans and animals can ingest varying amounts of the growth material and/or toxins. Even very small pieces of the cyanobacterial growth may contain enough anatoxin-a to cause medical emergencies. These pieces of bacteria may be hard to see or even invisible.

Scientist sampling cyanobacteria in the Virgin River
Scientist sampling cyanobacteria in the Virgin River


cyanobacteria growth on rock
Cyanobacteria forms shelves at the waterline including bulbous growths as seen here.


Last updated: March 24, 2021

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Zion National Park
1 Zion Park Blvd.
State Route 9

Springdale, UT 84767


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