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

UPDATE July 21, 2020

The Utah Division of Water Quality (DWQ), the Utah Department of Health (DOH), the National Park Service received updated sample results from the U.S. Environmental Protection Agency Region 8 lab in Denver on Wednesday, July 15 from the North Fork of the Virgin River. These results show anatoxin-a concentrations greater than 550 micrograms per liter in some samples of the cyanobacteria. Toxins were not detected in the water column. Cyanotoxin levels detected in the cyanobacterial growth are currently much greater than the DWQ/DOH recommended danger advisory threshold for cyanotoxins dissolved in water. 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 cyanotoxin to cause harm and these pieces may be invisible.

Some cyanobacteria may produce dangerous liver and 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.

Children are especially susceptible to this cyanotoxin.

Anatoxin-a can be absorbed through eyes, nose, or mouth by swimming in or submerging accidentally or unknowingly into contaminated water. Symptoms include skin rash, salivation, drowsiness, tingling, burning, numbness, pain, incoherent speech, vomiting, and diarrhea.

The likely cyanobacteria blooming in the Virgin River is MicrocoleusTychonema. It forms colonies that can be red, yellow, tan, green, brown, or black in color. It produces the cyanotoxin called anatoxin-a, which impacts the nervous system. The toxin was detected at levels in the park far above the recommended health threshold for primary recreation (swimming) at multiple locations.

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.

Last updated: July 21, 2020

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