SIESTA KEY, Fla. — Even as she sat under the brilliant Florida sun, her toes covered in sugar-white sand, Alex McShane wasn’t exactly enjoying her summer vacation. Florida’s worst red tide in more than a decade had turned the aqua-blue surf to a rusty dull brown.

And then there were the lifeguards. They were wearing gas masks.

With no mask of her own, McShane, 24, wore a frown. Her eyes itched, she coughed, and the stench was giving her a headache – all telltale symptoms of the monster algal bloom spanning the southern Gulf Coast. It is killing untold numbers of marine animals from Bradenton to Naples, where rotting fish still lie scattered on a beach behind Gov. Rick Scott’s seaside mansion, even after a cleanup.

As the outbreak nears the year mark, with no sign of easing, it’s no longer a threat to just marine life. Business owners in the hardest-hit counties report they have lost nearly $90 million and have laid off about 300 workers because of the red tide and a separate freshwater algal bloom in the state’s largest lake. Together, the two blooms have caused a sharp drop in tourism.

A pair of toxic algal blooms at the same time is rare and, in this case, especially lethal. A red tide is a natural phenomenon that develops miles offshore before making its way to the coast, where it feeds on a variety of pollutants, including phosphorus and nitrogen from fertilizer, along with other runoff and wastewater.

What is not clear is whether climate change and pollution from humans near the shore has made this outbreak even worse. Scientists have found that the algae thrive in warmer waters and increased carbon dioxide levels.

August has been brutal for Sarasota County, where McShane sat on a folding chair on the top-rated beach at Siesta Key. In the second week of the month – one of the worst of the red-tide bloom – small-business revenue fell by as much as 50 percent, according to a survey conducted by the local convention and visitors bureau.

State officials say the economic impact is expected to worsen as the outbreak continues.

McShane, who traveled from Ellicott City, Maryland, with her parents for a week-long visit, scanned the nearly deserted beach, which reeked like a commode that hadn’t been flushed.

“I definitely wouldn’t go in the water,” she said. “This is as close as I’m getting.”

Ten miles away at the Mote Marine Laboratory and Aquarium, Gretchen Lovewell and her two-woman crew responded to yet another emergency distress call.

They climbed into a pickup truck and rushed to Manasota Key Beach, an hour’s drive south, where a baby dolphin was spotted on the edge of the surf. The calf was dead, but its carcass could yield valuable tissue samples that would add to the understanding of how the toxin kills.

The red tide’s poisonous algae is a variety called Karenia brevis that is native to the Gulf of Mexico. It breaks out every year, and its neurotoxin disorients and paralyzes marine life. But in her nine-year tenure at Mote, Lovewell has never seen animals die on this scale.

As of Friday, the aquarium had recovered 19 dolphins and 239 sea turtles in Sarasota and Manatee counties alone. That did not include more than 100 manatees statewide and an untold number of fish, including sharks and tarpons.

To keep up with the death toll, Lovewell has worked six-day weeks and up to 16 hours on some shifts.

More than 2,000 tons of dead marine animals have been removed from the coasts of five counties. The baby dolphin was the 13th recovered.

“It definitely takes a toll on you, dealing with so much death,” Lovewell said. “When this is all said and done, I’m going to have to go into a room and scream and cry a little.”

The solution, environmentalists say, is prevention.

“We don’t have an algae problem in Florida,” said Andy Mele of Suncoast Waterkeeper, a nonprofit watchdog. “We have a nutrient problem.”

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