Toxic algae populations decreased markedly during last week’s stormy weather, but officials say residents should stay out of the water for a few more weeks, until further tests can confirm whether the coast is clear.
Ben Holcomb, a Utah Department of Environmental Quality algae specialist, said cell counts in samples collected from four locations on the lake Thursday topped out at about 5,000 cells per milliliter. Previous samples were as high as half a million cells per milliliter, he said.
However, Holcomb said three of the four sites tested positive for anatoxin, a deadly neurotoxin sometimes produced by cyanobacteria, the microorganism responsible for toxic blooms. Subsequent tests did not find the toxin, suggesting that the initial results may have been false positives.
“Laboratory techniques and science of how to detect this toxin are still, in my opinion, elementary and continue to develop,” Holcomb said. “We’re exploring why we’re getting some differences in results from those.”
Aislynn Tolman-Hill, a spokeswoman for the Utah County Health Department, said signs warning residents to stay out of the water at Utah Lake would remain, pending further tests over the next two weeks to confirm that the bloom is on its way out. Portions of the lake have been under the advisory since June 30, and the warning has expanded to include parts of the Jordan River.
Advisories related to E. coli at Sandy Beach also remain in effect, Tolman-Hill said.
She said the health department was hopeful about removing the algae-related advisory, which allows boating but warns against swimming, wading and other activities that would lead to direct contact with the water.
“We are cautiously optimistic at this point,” Tolman-Hill said.
It is possible for the algae to resurge, Holcomb said. Cyanobacteria are present in most natural waterways, and blooms develop when the conditions in a body of water allow for the rapid expansion of their populations. Blooms are most likely to develop in warm, stagnant water with nutrients available to feed the algae.
Depending on what the weather does as fall approaches, Holcomb said, data from past blooms suggests that the algae could return as late as October.
“Based on past years, I would expect it to show up again somewhere,” he said.
But the first bloom on the lake, he said, is typically the largest. Should the algae return, he said, the bloom likely would not cover as much of the lake as the current one.
“But it could be totally different because we’re living in a different world where the weather is concerned,” he added.
Whether or not the bloom returns this fall, Holcomb said, if the algae continue to lie low for the next few weeks, signs are likely going to come down, at least temporarily.
“If it’s going to stay silent for a little while,” he said, “then we can be comfortable with removing the warning.”
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