The Mysterious Dog-Killing Bacteria Plaguing a Popular National Park

Zion National Park is one of the country’s, if not the world’s, natural wonders. In Eastern Utah, the park is the 10th most visited national park according to the National Park Service (NPS), and throughout the pandemic continually struggled with overcrowding, with many hikers flooding in to cram themselves onto one hiking trail in particular: the Narrows.

The Narrows, aptly named, is the narrowest part of Zion Canyon. Hiking through it involves sloshing through the Virgin River, surrounded by huge rock faces on either side.

But a few weeks ago, the park was forced to warn visitors against the Narrows along with another popular hike, due to a toxic bacteria spreading through the park's waterways.

In a statement, the NPS wrote, “Toxin producing cyanobacteria has been detected in the North Fork of the Virgin River which will remain at a Warning Advisory.” It added: “During Warning and Health Watch advisories, recreators should avoid primary contact recreation such as swimming or submerging the head. During Danger advisories, recreators should consider avoiding all direct contact with the water.”

This isn’t the first national park or national recreation area to deal with a water problem. Earlier this year at the Grand Canyon 202 visitors got sick with norovirus, which lived in the river’s tepid water, and the Everglades have consistently struggled with algal blooms, otherwise known as red tides.

And even more surprising is that this isn’t the first time bacteria forced the Narrows to close. Two years ago, a dog died within one hour of swimming in the river and “snapping” at algae growing on the rocks. It couldn’t walk and was having seizures before its death, McClatchy News previously reported.

Dr. Kate Fickas, an aquatic biologist who worked with the U.S. Geological Service in Zion two years ago when this first sprung up but is now focused on South Dakota, said that at first they were baffled at what had caused the death of the dog.

“Oftentimes, dogs just drink water too fast, and so we thought it was just that,” she said.

However, after testing they found the water to contain cyanobacteria, commonly known as blue-green algae, the very same results the park discovered only a couple of weeks ago.

It’s not entirely uncommon. Dangerous blue-green algal blooms sprout up all over the country during higher temperatures. Take the Great Lakes for example, where harmful algal blooms are a common occurrence. Earlier this year, The New Scientist reported that harmful algal blooms are becoming increasingly common, worldwide.

Environmentalists are concerned, arguing that the sheer number of national parks with damaged water sources leaves a lot of questions to be answered. “More than half of the national parks have waters considered impaired” under the Clean Water Act, Sarah Gaines Barmeyer, deputy vice president for conservation programs at the National Parks Conservation Association, told The National Park Traveler, citing pollution coming from outside the parks as a main cause of impaired water quality.

However, there are a few things that make the algae in Zion a stranger case than most. The first is that algal blooms most commonly occur in lakes, large standing bodies of water; but in this case, an algal bloom occurred in a river.

“Algal blooms don’t often happen in rivers,” says Fickas, adding that “they especially don’t happen in pristine rivers.”

One of the biggest causes of algal blooms is runoff from fertilizers in nearby towns. When a large body of water isn’t dispersing these organisms via movement, they accumulate and that’s when you end up with blooms. In Zion, this isn’t a possibility, so scientists knew this algae was slightly out of the norm.

“So we began to hypothesize that the algae was benthic,” Fickas said. Benthic cyanobacteria differ from typical algae insofar as they live closer to the floor of the water body, instead of floating atop the surface. It also implies that the algae has always been a part of the river, they just haven’t bloomed, or been detected and become a source of heath concern, historically.

As for what is causing them to bloom two years ago and just a few weeks ago, scientists have some theories, although not much research has been done on the topic.

“An increase in water temperature would be problematic in theory,” says Dr. Don Bryant, a professor emeritus of biotechnology at Pennsylvania State University. “This problem would be greatest in the summer and in any drought seasons, which of course is continual now in the West.”

Another theory, according to the park, suggests high-flow events might trigger rapid regrowth. A spokesperson for Zion said, “National Park Service scientists have observed that high flow events (e.g., spring snowmelt or flash floods) scour away cyanobacteria. Following high flow events, park scientists have observed cyanobacteria regrowth happen in the following weeks and months.”

But determining the cause of the bacteria is only half the battle, of course. And while the bacteria is likely difficult to get rid of, according to Bryant due to it being part of the natural flora of the river, the National Park Service is instead turning its attention to continual sampling and testing, as well as alerting the public through various means.

In a statement to The Daily Beast, a spokesperson for Zion National Park outlined their efforts.

“In partnership with Utah Department of Environmental Quality (Utah DEQ) and the Utah Department of Health & Human Services (Utah DHHS), we issue health advisories so that visitors can make informed decisions about recreating in the park. We share updates about cyanobacteria on our park website, in social media posts, and in-person at park visitor centers, on trails, and in ranger talks. In all of these updates, we remind visitors not to drink or filter water from the North Fork of the Virgin River, La Verkin Creek, or North Creek.”

But Bryant’s view is that recreators shouldn’t be too worried. At least not yet. “One of the more interesting things to think about,” said Bryant, “is that many of the bacterias we’re finding have always been there. We’ve just gotten more diligent about testing them and telling people where it’s safe to swim.”

“I’ll put it this way,” Bryant continued. “I grew up swimming in lakes and ponds, and I don’t think much has changed about them. But would I swim in them today knowing what I know now? Absolutely not.”