This webpage is updated monthly with information provided by Zion National Park. The Utah Division of Water Quality does not routinely conduct HAB sampling within the Virgin River Watershed. If you have additional questions, please contact Zion National Park by calling (435) 772-3256.
This webpage is updated with information provided by Zion National Park.
Updates
Lower Virgin River:
Check for mats
October 25, 2025: Harmful algae mats monitoring update
CHECK FIRST: Our monitoring team observed a small number of harmful algae mats. Direct contact with or ingestion of mats can make humans and animals sick. Avoid mats while you recreate.
- Do not touch or eat any algae mats
- Keep children away from any algae mats
- Keep animals away from any algae mats
- Wading, fishing, and paddling are OK
- Know how to recognize a harmful algae mats
North Creek (including “The Subway”):
Check for mats
September 3, 2025: Harmful algae mats monitoring update
CHECK FIRST: Harmful algae mats may be present. Direct contact with or ingestion of mats can make humans and animals sick. Avoid mats while you recreate.
- Do not touch or eat any algae mats
- Keep children away from any algae mats
- Keep animals away from any algae mats
- Wading, fishing, and paddling are OK
- Know how to recognize harmful algae mats
North Fork of Virgin River (including “The Narrows”):
Warning Advisory
September 2, 2025: Harmful algae mats monitoring update
BE CAREFUL: Harmful algae mats are present. Direct contact with or ingestion of mats can make humans sick and may be lethal for dogs.
- Keep dogs and young children away from the water
- Do not touch or eat any algae mats
- Don’t filter drinking water here
- Wading, paddling, and fishing are OK
- Know how to recognize harmful algae mats
North Creek (including “The Subway”):
Warning Advisory
August 18, 2025: Harmful algae mats monitoring update
BE CAREFUL: Harmful algae mats are present. Direct contact with or ingestion of mats can make humans sick and may be lethal for dogs.
- Keep dogs and young children away from the water
- Do not touch or eat any algae mats
- Don’t filter drinking water here
- Wading, paddling, and fishing are OK
- Know how to recognize a harmful algae mats
North Fork of Virgin River (including “The Narrows”):
Warning Advisory
August 18, 2025: Harmful algae mats monitoring update
BE CAREFUL: Harmful algae mats are present. Direct contact with or ingestion of mats can make humans sick and may be lethal for dogs.
- Keep dogs and young children away from the water
- Do not touch or eat any algae mats
- Don’t filter drinking water here
- Wading, paddling, and fishing are OK
- Know how to recognize a harmful algae mats
La Verkin Creek:
Check for mats
August 18, 2025: Harmful algae mats monitoring update
CHECK FIRST: Harmful algae mats may be present. Direct contact with or ingestion of mats can make humans and animals sick. Avoid mats while you recreate.
- Do not touch or eat any algae mats
- Keep children away from any algae mats
- Keep animals away from any algae mats
- Wading, fishing, and paddling are OK
- Know how to recognize a harmful algae mats
Lower Virgin River:
Check for mats
August 18, 2025: Harmful algae mats monitoring update
CHECK FIRST: Our monitoring team observed a small number of harmful algae mats. Direct contact with or ingestion of mats can make humans and animals sick. Avoid mats while you recreate.
- Do not touch or eat any algae mats
- Keep children away from any algae mats
- Keepimals away from any algae mats
- Wading, fishing, and paddling are OK
- Know how to recognize a harmful algae mats an
La Verkin Creek:
Check for mats
August 5, 2025: Harmful algae mats monitoring update
CHECK FIRST: Our monitoring team observed a small number of harmful algae mats. Direct contact with or ingestion of mats can make humans and animals sick. Avoid mats while you recreate.
- Do not touch or eat any algae mats
- Keep children away from any algae mats
- Keep animals away from any algae mats
- Wading, fishing, and paddling are OK
- Know how to recognize a harmful algae mats
North Fork of Virgin River (including “The Narrows”):
Check for mats
July 15, 2025: Harmful algae mats monitoring update
BE CAREFUL: Harmful algae mats are present. Direct contact with or ingestion of mats can make humans sick and may be lethal for dogs.
- Keep dogs and young children away from the water
- Do not touch or eat any algae mats
- Don’t filter drinking water here
- Wading, paddling, and fishing are OK
- Know how to recognize a harmful algae mats
La Verkin Creek:
Check for mats
Monitoring for harmful algae on July 8, 2025
Harmful algae mats (benthic cyanobacteria) may be present. Avoid touching or disturbing algae mats. Avoid primary contact recreation (swimming and submerging the head) when recreating in this area. Do not drink in-stream water anywhere in the park. If you must filter water, do so directly from a spring source.
La Verkin Creek:
Check for mats
Monitoring for harmful algae on July 8, 2025
Harmful algae mats (benthic cyanobacteria) may be present. Avoid touching or disturbing algae mats. Avoid primary contact recreation (swimming and submerging the head) when recreating in this area. Do not drink in-stream water anywhere in the park. If you must filter water, do so directly from a spring source.
Lower Virgin River:
Check for mats
Monitoring for harmful algae on July 8, 2025
Harmful algae mats (benthic cyanobacteria) may be present. Avoid touching or disturbing algae mats. Avoid primary contact recreation (swimming and submerging the head) when recreating in this area. Do not drink in-stream water anywhere in the park. If you must filter water, do so directly from a spring source.
Lower Virgin River:
Looks Good
Monitoring for harmful algae on June 23, 2025
GOOD NEWS: Our monitoring team did not see any visible signs of harmful algae mats (benthic cyanobacteria) at the recreational sites they visited. However, mats may be present at other sites or regrow before our next visit. Know what to look for and check before letting children or pets in the water.
North Creek (including “The Subway”):
Warning Advisory
Recent monitoring on June 17, 2025
Harmful algae mats (benthic cyanobacteria) are present and producing toxins. Avoid touching or disturbing algae mats. Avoid primary contact recreation (swimming and submerging the head) when recreating in this area. Do not drink in-stream water anywhere in the park. If you must filter water, do so directly from a spring source.
North Fork of Virgin River (including “The Narrows”):
Warning Advisory
Recent Monitoring on June 16, 2025
Harmful algae mats (benthic cyanobacteria) are present and producing toxins. Avoid touching or disturbing algae mats. Avoid primary contact recreation (swimming and submerging the head) when recreating in this area. Do not drink in-stream water anywhere in the park. If you must filter water, do so directly from a spring source.
La Verkin Creek:
Health Watch
Recent Monitoring on June 16, 2025
Harmful algae mats (benthic cyanobacteria) may be present. Avoid touching or disturbing algae mats. Avoid primary contact recreation (swimming and submerging the head) when recreating in this area. Do not drink in-stream water anywhere in the park. If you must filter water, do so directly from a spring source
Lower Virgin River:
Looks Good
Monitoring for harmful algae on June 6, 2025
GOOD NEWS: Our monitoring team did not see any visible signs of harmful algae mats (benthic cyanobacteria) at the recreational sites they visited. However, mats may be present at other sites or regrow before our next visit. Know what to look for and check before letting children or pets in the water.
North Creek (including “The Subway”):
Warning Advisory
Monitoring for harmful algae on October 1, 2024
Harmful algae mats (benthic cyanobacteria) are present and producing toxins. Avoid touching or disturbing algae mats. Avoid primary contact recreation (swimming and submerging the head) when recreating in this area. Do not drink in-stream water anywhere in the park. If you must filter water, do so directly from a spring source.
North Fork of Virgin River (including “The Narrows”):
Warning Advisory
Monitoring for harmful algae on October 1, 2024
Harmful algae mats (benthic cyanobacteria) are present and producing toxins. Avoid touching or disturbing algae mats. Avoid primary contact recreation (swimming and submerging the head) when recreating in this area. Do not drink in-stream water anywhere in the park. If you must filter water, do so directly from a spring source.
La Verkin Creek:
Health Watch
Monitoring for harmful algae on October 2, 2024
Harmful algae mats (benthic cyanobacteria) may be present. Avoid touching or disturbing algae mats. Avoid primary contact recreation (swimming and submerging the head) when recreating in this area. Do not drink in-stream water anywhere in the park. If you must filter water, do so directly from a spring source.
Since July 2020, the National Park Service (NPS) in Zion National Park has been monitoring harmful algal bloom (HAB) toxin production on a monthly basis at several water bodies inside the park.
Cyanobacteria and HABs in the Virgin River are different from what is commonly seen in Utah’s lakes and reservoirs. This cyanobacteria grows in mats on the bottom of the riverbed, often attached to rocks or plants. It may be brown, black, tan, or green and comes in a variety of textures.
How can I stay safe while recreating in Zion National Park?
Why are habs in zion national park dangerous?
Cyanobacteria living in the Virgin River (including “The Narrows” and other locations in Zion Canyon) may produce dangerous toxins. These toxins target the liver and nervous system and are dangerous for people and animals.
Toxins can be absorbed through eyes, nose, or mouth by swimming in contaminated water – very small or even invisible pieces of the cyanobacterial growth may contain enough toxin to cause harm.
What are the symptoms of HAB exposure?
Symptoms of toxin exposure include:
If you think you have been exposed, immediately contact the Utah Poison Control Center at (800) 222-1222.
How does Zion National Park determine exposure risk?
The NPS, DWQ, and Utah Department of Health and Human Services have worked to characterize exposure risk from HABs in the Virgin River in order to better compare toxin results to the current DWQ/DHHS HAB Guidance and Recreational Thresholds.
Zion National Park staff rely on three lines of evidence for issuing recreational advisories:
- The presence or absence of known toxin-producing cyanobacteria species.
- The presence or absence of toxins in the water body using SPATT bags.
- ‘Benthic disturbance sampling’ – a process where a water quality scientist walks along a cyanobacterial mat (imitating recreation) and then measures the concentration of toxins produced.