A warning about harmful cyanobacteria and cyanotoxins in the North Fork of the Virgin River in Zion National Park continues to be in effect — and the problem is expected to get worse because of the extreme heat and ongoing drought.
The warning includes The Narrows, the popular hiking area in the park that is only accessible by walking in the river.
While toxic algal blooms were once thought to be restricted to lakes, ponds and reservoirs, they’re now being found in rivers. The staff at Zion began monitoring the Virgin River after a reported pet death there in July 2020, and issued an advisory last year. It was downgraded to a warning in May, but experts warn conditions are ripe for the toxins to increase.
The bacteria “really like warm weather,” said Kate Fickas, aquatic biologist and environmental scientist with the Utah Department of Environmental Quality. “Colder waters are sometimes harder for them to survive in.”
Plus, the only way to treat the bacteria in rivers is “large scouring events that occur after rainfall” — and the state is in the midst of a severe drought.
“Zion National Park received almost no rain last year, not enough to scour,” Fickas said. “So with the drought forecast looking worse and worse, combined with a lack of [rain], we’re potentially looking at an advisory on both sides of park boundaries all summer long.”
The problem is varieties of cyanobacteria, “which are a mix between a bacteria and a plant that can produce these really toxic chemicals” that can be “neurological and liver damaging,” Fickas said. And finding them on the bottoms and sides of rivers is “a new phenomenon. Utah is really only the second state in the country to be ahead of these types of bacteria blooms that are distinctly different from blooms within lakes and reservoirs.”
“It’s a real risk to recreators,” said Robyn Henderek, physical science program manager at Zion National Park. Anyone can be exposed, even “a child who’s sitting on the edge of the river, playing in the water, stacking rocks.”
Under the current warning advisory, with tests showing in excess of 15 micrograms per liter of the toxins, park goers are advised to avoid “primary contact” with the water — no swimming, and avoid submerging your head and splashing. At the moment, North Fork is “relatively low risk,” Henderek said, but visitors should not drink from any streams in the park, and there are no recreational filtering systems known to remove the toxins.
Symptoms can include, but are not limited to: Skin rash, salivation, drowsiness, tingling, burning, numbness, pain, incoherent speech, seizures, vomiting and diarrhea. Children are especially vulnerable to the toxins, and dogs should be kept on leashes and out of the water.
If the level of toxins rises to 90 micrograms per liter, the park will issue a danger advisory cautioning against any contact with the water.
North Creek is also under a warning advisory because of the presence of cyanotoxins. A health watch has been issued for La Verkin Creek because of the presence of harmful cyanobacteria.
State authorities also believe it’s possible the toxins have spread south, outside Zion, to such areas as Rockville and Springdale.
“We’ve seen some visual assessments showing really small populations of ... possibly toxic cyanobacteria south of Rockville,” Fickas said. “We actually found low levels of toxins flowing through there as of last year. However, conditions can change. The drought’s gotten worse. So we’re not able to characterize with confidence in terms of an exact risk at each different geographic location. … There’s always recreational risk to residents of Springdale and Rockville.”
However, she said, they have found “absolutely no detection of toxins in the drinking water or in irrigation waters,” which are frequently monitored.