Officials warn of potentially harmful algal bloom in Mantua Reservoir

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MANTUA — Officials are warning visitors to Mantua Reservoir in Box Elder County of a potentially harmful algal bloom that has been found in the water.

The algal bloom was discovered Monday along the west beach and dock.

"It kind of takes the form of an oil sheen on the top. It's a greenish oil-looking sheen," said Mack Stokes, an environmental health scientist for the Bear River Health Department. "It can be really thick, and it can be really thin. It just depends on the time of day and time of year."

Stokes visited the reservoir Tuesday to investigate the bacteria.

Stokes said samples of the bacteria were taken Tuesday morning but results showing just how toxic it is won't be available for several days, perhaps as early as Friday.

"If those toxin levels in those samples exceed certain thresholds, then we will take action," Stokes said.

If the bacteria exceed the safe threshold, the reservoir will likely close. Until those results are known, as a precaution, the Bear River Health Department issued a warning to visitors to stay out of the water.

"If the conditions are just right, if there is enough nutrients like phosphorous and nitrogen, those bacteria will multiply really quickly," Stokes said.

Ingesting the potentially dangerous cyanobacteria can cause serious health issues for people and pets.

"If you're ingesting a concentrated portion of that bloom, that could cause serious gastrointestinal issues like nausea and vomiting. If you were to ingest enough of it, it could get you hospitalized or even cause death, but we rarely see instances like that," Stokes said.

Mantua Reservoir in Box Elder County is seen on Tuesday. Officials are warning of a potentially harmful algal bloom at the reservoir. (Photo: Mark Less, KSL-TV)

KSL-TV spoke with several families enjoying Mantua Reservoir Tuesday who said they were unaware of a potentially toxic algal bloom developing in the water.

"I had no idea," said Heather Burke, who was watching her children on kayaks and paddle boards.

"We tried to talk to the kids to see if they drank the water because I'm concerned about that now, and some have," said Chamberlee DeGraff, Burke's sister.

The Bear River Health Department posted small signs about the new potentially harmful algal blooms around the reservoir Monday night – but visitors Tuesday expressed frustration with visibility. The Bear River Health Department said the signage will be evaluated to determine if more visible signs should be posted. The health department also issued warnings about the algal bloom on its social media pages and its website.