An undated photo of cyanobacteria that formed in the Virgin River with shelves at the waterline including bulbous growths.

National Park Service

Zion National Park issues danger advisory over harmful algal bloom

By Carter Williams, | Posted - Mar. 25, 2021 at 11:33 a.m.

SPRINGDALE, Washington County — Zion National Park visitors are being asked to avoid any contact with the North Fork portion of the Virgin River "until further notice" due to a worsening toxic algae bloom.

Park officials on Tuesday said a danger advisory for the region was issued due to growing levels of cyanobacteria. The danger advisory applies to places within the park from the Zion National Park Visitor's Center northward, according to the Utah Division of Water Quality. Park officials said that includes The Narrows.

Algal blooms are harmful because they can produce cyanobacteria and cyanotoxins, which can cause rash, salivation, drowsiness, tingling, burning, numbness, pain, incoherent speech, seizures, vomiting and diarrhea. It's also potentially fatal in humans, pets and livestock.

"Even very small pieces of the cyanobacterial growth may contain enough anatoxin-a to cause medical emergencies," park officials wrote. "These pieces of bacteria may be hard to see or even invisible."

Under the danger advisory, experts said children — who are "especially vulnerable" to cyanotoxins — should not be in contact with affected water bodies. They also advised that visitors do not submerge their heads in the water because the toxins can enter the body through the mouth, nose, eyes or any open wounds.

In addition, visitors are being asked to not drink the river water because there is no known recreational filtration system that could effectively clear the cyanotoxin from the water. Park officials said some permitted activities will be allowed to continue, including technical canyoneering.

Pets should also be kept away from the water.

"Dogs must be kept on a leash. If pets get into the river, remove them from the water immediately, rinse off their fur thoroughly, and monitor for symptoms of toxin poisoning," officials with the Utah Division of Water Quality wrote in an alert Wednesday. "A dog can die in as little as 15 minutes from anatoxin-a poisoning."

Park staff first started monitoring for cyanobacteria last year after a pet died from the toxic algae. They looked for cyanobacteria and cyanotoxins at three major tributaries of the Virgin River: North Fork, North Creek and La Verkin Creek.

All three had low levels of cyanobacteria at the time but that changed in the North Fork area this month.

"Detected toxin concentrations have increased in the North Fork of the Virgin River to a level that poses a risk to recreators," park officials wrote. "Visitors are encouraged to avoid all contact with the water until further notice."

A warning advisory was also issued for North Creek and a health watch was issued for La Verkin Creek, according to park officials. While levels of cyanobacteria weren't as high, some of the recommendations were similar to the North Fork.

"Visitors should avoid primary contact (i.e. swimming or submerging your head) with water in North Creek and La Verkin Creek," they wrote. "Visitors should not filter drinking water from any streams in the park until further notice."

Park officials added that the cyanobacteria colonies may appear red, yellow, tan, green, brown, or black in color. They urged anyone with concerns about anatoxin-a poisoning to call the Utah Poison Control Center at 800-222-1222 and 911 in the case of a medical emergency.

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