FRESNO, Calif. — Toxic algae has been found in a Yosemite creek and the National Park Service is warning guests it may exist in other spots in Yosemite Valley.

In an Instagram post Friday, the park service said recent tests at the park in Central California yielded positive results for small amounts of the algae, which can have concentrated levels of toxins that are released into the water when the algae dies or is disturbed.

The toxins are known to have harmful effects and are one possible theory in the mysterious death of a family and their dog in the nearby Sierra National Forest last month, near the Highway 140 entrance to Yosemite.

“For your safety, do not enter or drink from Tenaya Creek, which flows from above Mirror Lake to where it enters the Merced River near North Pines Campground,” the Park Service post read.

The park service said that some sites may have warning signs up, but guests should remain cautious; they are asked to report any large blooms or algae that is “particularly bright, bubbly, strange-looking, or appears like a haze in the water.”

Clear water with no visible algae is low risk, but isolated clumps of floating algae can still be present. The park service asks that guests not disturb algal mats in any way.

“Wading or swimming can cause toxins to be released into the water.”

The state health department reported that animals have been poisoned from algae and people should prevent pets from drinking from affected waters or eating or touching the algae, even it’s on shore. At high levels, the algae can cause diarrhea, vomiting and other affects in people, but “no known human fatalities have been documented from recreational or drinking water exposure to cyanobacterial toxins,” in the algae.

The park service is continuing to monitoring for other toxic algae sites and testing for toxins throughout the park.

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