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

 
Cyanobacteria that is yellow in color with a vein like appearance growing on the bottom of the river
Cyanobacteria can grow on surfaces like rocks, sticks, and sand. The yellow/brown, vein textured material in this photo is cyanobacteria.

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Zion National Park is monitoring for the presence of toxic cyanobacteria and cyanotoxins in water throughout the park. We share information so you can make informed decisions about whether and how to recreate. We work with the Utah Department of Environmental Quality to share recreational advisory levels for still and flowing water throughout the park. Recreational advisory levels are:

  • Health Watch
  • Warning
  • Danger

Learn more about how the Utah Department of Environmental Quality sets these levels. The National Park Service shares current recreational advisory levels for Zion on this page.

Need to know:

Do not drink stream water anywhere in the park. Carry water or filter directly from a spring

 

Waterbody

Popular Areas Affected

Recreational Advisory Level

North Fork of the Virgin River

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

Warning

North Creek (Tributary of Virgin River)

Right Fork
Left Fork (The Subway)
Grapevine Spring
All canyoneering routes with an active surface water connection to North Creek

Warning

La Verkin Creek (Tributary of Virgin River

La Verkin Creek
Timber Creek
Hop Valley Creek
All canyoneering routes with an active surface water connection to La Verkin Creek

Health Watch

This table shows the current recreational advisory level for each monitored waterbody in the park. During Health Watch and Warning advisory levels we recommend against swimming or submerging your head in the water. During Danger advisory levels recreators should consider avoiding all contact with the water.

 

Frequently asked questions

If you may have been exposed to toxin-producing cyanobacteria and have any unexplained symptoms, seek immediate medical attention and contact the Utah Poison Control Center by calling (800) 222-1222. If you are experiencing a medical emergency call 911.    

No. There are no known recreational filtration or disinfection method that can remove cyanotoxins from the water so that it is safe for drinking. If you must filter water for drinking while in the Wilderness areas of the park, do so directly from a spring source. 

Symptoms in a humans can include, but are not limited to, irritation in the ears, eyes, nose, skin, or throat. You could also experience a headache, burning, tingling, numbness, pain, incoherent speech, seizures, vomiting and/or diarrhea.  
 
Symptoms in pets can include, but are not limited to, drooling, low energy, lack of appetite, stumbling, paralysis, tremors, and/or vomiting. 

Scientist’s understanding of benthic cyanobacteria is evolving. Our understanding of benthic cyanobacteria and the risk it poses to human health are changing with new information. The park uses the best available science and considers the most vulnerable populations (Children and pets) when it sets recreational advisories. 

The risks are unknown. Check recreational advisory levels to make informed choices about recreation in Zion.   

Toxin-producing cyanobacteria naturally live in waterbodies throughout the world and in Zion, however, during extended periods of time without flood events toxin-producing cyanobacteria tend to grow in proliferation. When cyanobacteria have the opportunity to grow in large amounts the risk of harm to humans and domestic animals increases.

 
brown cyanobacteria attached to the side of the river.
Cyanobacteria attached to the side of the river in Zion. Note the yellow/brown color and vein like texture

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More About Cyanobacteria

An introduction

Cyanobacteria also known as “blue green algae”, are photosynthetic bacteria found in lakes, reservoirs, rivers, streams, and other bodies of water in many places throughout the world. In other waterbodies, cyanobacteria are found on the top of the water or dispersed throughout the water column. In Zion, scientists have found cyanobacteria at the bottom of the Virgin River and its tributaries within the park. The kind of cyanobacteria attached to the bottom of the river is known as benthic cyanobacteria. Benthic cyanobacteria grows on rocks, plants, at the sides of the river and along the river's edge

Why are cyanobacteria harmful?

Cyanobacteria are naturally occurring but can harm humans or animals because some produce toxins called cyanotoxins. Scientists have found anatoxin-a, microcystin, nodularin and cylindrospermopsin in the park.

According to the US Environmental Protection Agency, when people are exposed to cyanotoxins, they can experience a range of symptoms. These can include a mild skin rash, serious illness, or in rare circumstances, death. Severe (acute) illnesses caused by short-term exposure to cyanobacteria and cyanotoxins during recreational activities like swimming, include hay fever-like symptoms such as skin rashes, respiratory as well as neurological or gastrointestinal distress.

Drinking water contaminated with cyanotoxins (such as microcystin and cylindrospermopsin) could cause liver and kidney damage.

What to do if you are exposed to cyanobacteria

If you are exposed to cyanobacteria, seek immediate medical attention and contact the Utah Poison Control Center at (800) 222-1222. If you are experiencing a medical emergency, call 911.

 
symptoms of cyanobacteria: irritation in the ears, eyes, nose, skin, or throat. headache, burning, tingling, numbness, pain, seizures, vomiting, diarrhea.
Symptoms of exposure to cyanotoxins.

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Nostoc Physical description: Yellow, brown or black gelatinous pearls. Can be smooth or mossy in texture found growing on a rock
Cyanobacteria attached to a rock near the water's surface in Zion. Note the black color and round shape.

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Recognizing cyanobacteria

Cyanobacteria grow in different colors and textures. In Zion, these colors include yellow, tan, green, brown, and black and can appear to be round, ribbed, or mucous-like.

 
Cyanobacteria that is a yellow, squishy blobs that form mucous-like mats
Close up of cyanobacteria growing along the bottom of the river in Zion. Note the yellow color and globular texture.

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cyanobacteria
 
Cyanobacteria that is light brown in color, slimy, felt-like appearance. Veiny, but may not always have veins. Appears more bubbly on surface. Forms mats up to several centimeters thick
Cyanobacteria growing along the river's edge in Zion. Note the bubbly texture and brown color.

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cyanobacteria
 
cyanobacteria that is green in color with a feathery texture
Cyanobacteria growing at the bottom of the river on a rock in Zion. Note the green color and feathery texture.

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green cyanoabcteria with a feathery apperance growing on rock
 
cyanobacteria that is yellow in color growing on the bottom of the river
Cyanobacteria growing along the river's bottom in Zion. Note the yellow color and vein appearance.

NPS

Cyanobacteria growing along river bottom. Note the yellow vein appearance.
 
cyanobacteria that is growing on a rock
Cyanobacteria mat growing on a rock in the river in Zion.

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Where do cyanobacteria grow?

Cyanobacteria are photosynthetic and can grow in water anywhere sunlight can reach them. Benthic cyanobacteria can grow at the bottom of still and flowing water and can also grow attached to plants, rocks, and at the sides or edges of the river. Benthic cyanoabcteria often appear to form in mats but not always.

 
cyanobacteria mat growing along the side of the river
Scientist pulling off a piece of the cyanobacteria mat growing along the rivers edge in Zion.

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Scientist pulling off a piece of the cyanobacteria mat from the edge of the river.
 
cyanobacteria growing along plants on the edge of the river
Cyanobacteria growing alongside the edge of the river and on a plant.

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Cyanobacteria growing alongside the edge of the river and on a plant.
 

How is Zion Monitoring for cyanobacteria?

Park scientists monitor popular bodies of water for toxin-producing cyanobacteria and cyanotoxins. All data is shared with the Utah Department of Environmental Quality. Monthly monitoring data inform the recreational advisory level. Recreational advisory levels can be found on the park's website, at all visitor contract stations, and on signs posted at major trailheads.

Monitoring Techniques

Scientists perform visual inspections of selected sites in three major tributaries to the Virgin River in Zion National Park to determine if cyanobacteria are visually present. Additionally, we monitor if there are cyanotoxins within the water column, using a passive monitoring technique called SPATT samples (Solid Phase Adsorption Toxin Tracking). These samples are specially designed to monitor for the presence of toxins in the water column over a period of time. Lastly, if toxin-producing cyanobacteria mat are present, staff will perform a sampling technique called Benthic Disturbance. In Benthic Disturbance samples, staff walk through cyanobacteria mats replicating conditions expected when these mats are disturbed through normal recreational activities. Samples are then taken of the disturbed water and analyzed for their concentration of cyanotoxins.

 
Ranger holding cyanobacteria that has a mucous like texture. A picture of a SPATT sample submerged in the water surrounded by cyanobacteria. A ranger walking in a cyanobacteria mat to intentionally disturb cyanobacteria.
Cyanobacteria sampling techniques

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Check out our videos series below to learn more!

 
 
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Duration:
2 minutes, 52 seconds

The first in a series of three videos with information you need before recreating in still or moving water at Zion National Park.

 
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Duration:
1 minute, 51 seconds

Information about the cyanobacteria in the flowing and still water of Zion National Park and the types of cyanotoxins they produce that can be potentially harmful.

 
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Duration:
2 minutes, 21 seconds

Information on how scientist in Zion study and monitor cyanobacteria and cyanotoxins the Park's still and flowing water.

Last updated: November 7, 2023

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Contact Info

Mailing Address:

Zion National Park
1 Zion Park Blvd.

Springdale, UT 84767

Phone:

435-772-3256
If you have questions, please email zion_park_information@nps.gov. Listen to recorded information by calling anytime 24 hours a day. Rangers answer phone calls from 11:30 a.m. to 3 p.m. and 3:30 p.m. to 5 p.m. MT, but a ranger may not answer if they are already speaking with someone else.

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