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A bright yellow warning sign popped up along the eastern shore of Utah Lake on Wednesday, warning that toxic algae is possibly once again plaguing the waters.

The potentially poisonous blue-green bloom is growing in a miles-long slick from Provo Bay to Provo Harbor near Utah Lake State Park, making the water unsafe for recreation. The Utah Division of Water Quality advises that people and pets not swim in or drink from the lake "until further notice."

Though not all algal growth is harmful, some types contain cyanobacteria, which can cause headache, fever, diarrhea, abdominal pain, nausea, vomiting and allergiclike reactions with skin contact, according to a news release from the Utah Department of Environmental Quality. If ingested, it can be fatal.

"We certainly want people to be safe," DEQ spokeswoman Donna Kemp Spangler said about the potential health risks.

The bloom was previously seen on Utah Lake in 2014, when officials determined it was the cause of death for two dogs. This year's growth, Spangler said, is "pretty large" and runs east to west. Satellite imagery shows the algae covering about 100 square kilometers of the lake, according to the release.

A recreationist discovered the "heavy bloom" Wednesday morning and alerted authorities, said Erica Gaddis, assistant director of water monitoring with DEQ. Crews collected samples about 1 p.m. and sent them to the Environmental Protection Agency for testing. Pending further results, expected Friday afternoon, more advisories may be issued through the Utah County Department of Health.

Algae is a natural component of many lake ecosystems, but waters with high levels of nutrients, warm temperatures, calm flows and heavy sunlight can develop extensive blooms that pose a risk.

A triathlon scheduled for this weekend near Utah Lake may be moved to another venue, the release states, due to the growth.

ctanner@sltrib.com

Twitter: @CourtneyLTanner