Danger Advisory issued for harmful algal bloom at Mantua Reservoir

MANTUA, Box Elder County  — The highest warning level used for toxic algae in Utah has been issued for Mantua Reservoir in Box Elder County. Utah health officials are warning people to stay out of the water and to ensure that pets also stay out of the water. 

The Danger Advisory comes as Utah heads into another stretch of triple-digit temperatures, conditions that, according to state officials, can help harmful algal blooms develop and spread.

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The Utah Department of Environmental Quality advises people not to swim, wade or participate in other water activities at Mantua Reservoir while the Danger Advisory remains in effect.

Officials also warn against drinking the water or allowing pets to enter it.

What is a Danger Advisory?

A Danger Advisory is issued when testing shows harmful algal bloom toxins have reached levels that could pose a serious health risk.

Unlike lower-level advisories that may allow some recreation with caution, a Danger Advisory means people should stay out of the water entirely because exposure can make both people and animals sick.

The toxins produced by harmful cyanobacteria can cause skin irritation, stomach illness and, in some cases, more serious health problems.

Dogs face an even greater risk

While people are being urged to avoid the water, state officials say dogs are often the first victims of harmful algal blooms because they naturally swim, drink from lakes and lick water from their fur after leaving the shoreline.

“Dogs are particularly vulnerable because they love to play in bodies of water,” said Utah State Veterinarian Amanda Price. “When they go into the water, they’re going to come in contact with the toxins produced by these algae.”

Price said those toxins can damage several organs, including the liver, kidneys and brain.

She said pet owners should never assume their dog will be okay after swimming in contaminated water.

“Yes, absolutely. It can become life-threatening very quickly,” Price said. “If they see any signs in their animals after they’ve been in these waterways, they need to take their pet to the vet right away so treatment can begin.”

Veterinarians recommend owners watch for vomiting, diarrhea, weakness, stumbling, excessive drooling, seizures or other unusual behavior after a dog has been exposed to potentially contaminated water.

Heat creates ideal conditions for blooms

The Danger Advisory comes during one of Utah’s hottest stretches of the summer.

Price said warm temperatures help create the conditions necessary for algal blooms to grow, meaning Mantua Reservoir may not be the only waterbody affected in the coming weeks.

“These algal blooms love to bloom in warm water,” Price said. “This heat wave that we’ve been having is going to warm up that water. So yes, I would expect to see more of these in more waterways.”

While the Department of Environmental Quality routinely monitors lakes and reservoirs across the state, officials encourage visitors to check current water quality advisories before making plans to swim, boat or bring pets to the water.

What visitors should do

State officials recommend checking for harmful algal bloom advisories before heading to any Utah lake or reservoir, especially during extended periods of hot weather.

Even if an advisory has not yet been posted, Price said pet owners should use caution if they notice water that appears unusually green, blue-green, discolored or has surface scum.

“If you see anything suspicious, anything in the water that looks suspicious, try to keep your dog out of it,” she said. “Definitely keep them from drinking that water.”

The Utah Department of Environmental Quality will continue monitoring Mantua Reservoir and other waterbodies across the state. The Danger Advisory will remain in effect until testing shows toxin levels have fallen to safe levels.