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Utah’s toxic algal blooms persist as weather cools, may outlive health warning advisories

(Chris Detrick | Tribune file photo) A toxic algal bloom in Utah Lake, as seen on June 29, 2017. Although October typically marks the end of Utah's algae season, seven toxic blooms persist across the state, including one on Utah Lake.

Although October is generally thought of as the end of algae season, seven toxic algal blooms continue to overstay their welcome in Utah.

At Utah Lake west of Provo, where the year’s longest-lived algal bloom persists, health officials are making plans to remove warning signs that have remained in place all summer.

Test results received earlier this week from the lake indicate that the bloom continues to produce potentially harmful toxins, said Aislynn Tolman-Hill, a spokeswoman for the Utah County Health Department. But, since the lake’s peak recreation season is coming to an end and monitoring efforts are scaling back, the health department plans to remove its warning signs from the lake.

But the amount of cyanobacteria, also known as blue-green or toxic algae, in Utah Lake continues to warrant a warning advisory that recommends people avoid swimming in or otherwise coming into direct contact with the water, officials said.

Health officials did not issue restrictions on boating or other forms of recreation on the lake this year because the number of cyanobacteria remained consistently lower than in summer 2016, when the lake was closed.

Tolman-Hill said the health department is working on new educational materials to distribute in lieu of its lakeside warning signs.

Warning advisories related to elevated levels of harmful E. coli bacteria at a handful of locations on Utah Lake will remain in place, Tolman-Hill said. The source of the E. coli has not yet been located.

The team of graduate students from Brigham Young University who helped collect water samples from Utah Lake this year stopped monitoring the lake for algae earlier this month. Bon Holcomb, harmful algal bloom program coordinator for the state Division of Water Quality, said state scientists likely won’t check the lake for algae again until mid-November.

Algal bloom monitoring continues elsewhere in the state. Chris Smoot, a spokesman for Wasatch County Health Department, said officials there were going to continue testing for cyanobacteria until they were sure the blooms were gone.

Deer Creek Reservoir and Jordanelle Reservoir currently have active though relatively small algae blooms. Deer Creek has tested positive for a liver toxin known as microcystin, which can cause gastrointestinal distress. Jordanelle’s bloom has tested for anatoxin, a neurotoxin that can prove fatal if ingested.

Fortunately, Smoot said, both blooms are limited to a few locations and have not spread to cover the entire lake, as has been known to happen on Utah Lake.

Warning signs that advise against swimming at those locations will remain in place until the toxins are gone, Smoot said. Monitoring will likewise continue, he said, even if it means checking under the ice.

It’s unclear just how rare it is for algal blooms to persist this late in the year in Utah. Erin Jones, one of the BYU graduate students studying algae at Utah Lake, said little data are available on the phenomenon because most testing efforts end before this time of year.

“Traditionally, monitoring ends at this point whether the bloom is continuing or not,” she said, “because irrigation [water] supplies shut off Oct. 1 and recreation usually ends Labor Day weekend.”

Jones and Holcomb said it may not be abnormal for the algae to linger this late in the year.

Utah would need to see an extended period of subfreezing temperatures, a cold rain or some snow to sufficiently cool down water temperatures and rid itself of the blooms, Jones said. This fall’s weather, meanwhile, has been relatively mild, though neither September nor October were abnormally warm, according to the National Weather Service.

Charlotte Dewey, a National Weather Service forecaster based in Salt Lake City, said it was possible that extreme summer heat warmed up the lakes more than usual, meaning it may may take longer for them to cool. August, for example, averaged more than 4 degrees above normal.

Cold temperatures typically cause the algae to die off swiftly, so the blooms could come to an end in a week or two. Whether or not they persist, Holcomb said, the fact that they got an early start this year has made for a long bloom season.

“I would expect things to be quickly falling off here,” he said, “but we’re keeping an eye on things.”

In any case, Holcomb said, late-season blooms aren’t likely to pose a significant health threat “unless you’ve got a public that’s wanting to break ice to go swimming.”