ZION NATIONAL PARK (ABC4 News) — A hike through the Narrows may sound irresistible in near triple-digit heat, but rangers at Zion National Park recommend that visitors avoid all contact in the Virgin River until further notice amid an ongoing toxic algal bloom first detected earlier this summer.

The National Park Service and the Utah Division of Water Quality (DWQ) have been monitoring the cyanobacteria in the north fork of the Virgin River since July 7, when a 5-month-old husky puppy died within minutes from algal poisoning.

“The dog was snapping at it and potentially ate some of the algae,” chief of resources and research Cassity Bromley said. “That’s what triggered us to start testing and looking for this in the water.” 

Since then, scientists have detected the toxin-producing cyanobacteria at extreme levels, including in the Narrows section of the Virgin River.

“When you undertake the Narrows hike, you are committing to wading through water affected by this cyanobacteria. There is currently an elevated risk to entering the water. The river is not closed, but we recommend avoiding this risk altogether by simply not entering the water,” park officials wrote on its Facebook page.

The colonies of cyanobacteria produce the potent cyanotoxin called anatoxin-a, which impacts the nervous system. 

In some areas, researchers have collected samples from the mats in the river system with anatoxin-a concentrations greater than 550 micrograms per liter. The state’s recommended danger advisory threshold is 90 micrograms per liter.

Park officials tell ABC4 News they don’t know as much about possible impacts through intact skin, but getting it in your nose, mouth, and eyes is the most hazardous pathway by swimming or submerging into contaminated water. 

Children and dogs are thought to be particularly sensitive and warrant special vigilance. Symptoms of algal poisoning include skin rash, salivation, drowsiness, tingling, burning, numbness, pain, incoherent speech, seizures, vomiting, and diarrhea.

The drinking water in the town of Springdale is being tested daily, and anatoxin-A has not been detected, according to park officials. 

“Anatoxin-a was detected in La Verkin Creek and North Creek in the bacterial growth, however, samples were not collected of toxin levels after recreational disturbance so the levels of toxins cannot be equated to the DWQ/DOH advisory thresholds at this time,” park officials wrote.

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. Visit Utah Department of Water Quality for the most up-to-date information.