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The dead fish pile up like sand dunes in Tampa Bay. Holley Short has been watching them for weeks with growing apprehension. Every time a shorebird picks at one of the carcasses, she wants to chase it away. “It’s really easy pickings for them. But it’s so hazardous to their health,” she says.

As a shorebird project manager for , Short is in charge of monitoring several nesting colonies of Black Skimmers, along with the bay’s tern, pelican, and cormorant populations. Normally she worries about beachgoers and their pets accidently disturbing skimmer nests. This year, fish bathed in toxic algae have been on her list of concerns.

Harmful algal blooms—otherwise known as HABs or “red tides”—occur when toxic algae become highly concentrated in ocean waters. Tampa Bay is currently in the grip of an intense bloom, which has resulted in more than 900 tons of dead fish and other marine debris being removed from beaches as of last week,  to the Pinellas County Department of Solid Waste. The tide currently extends from Pasco county down to Cape Coral. As the situation worsens, dozens of organizations for Florida Governor Ron DeSantis to declare a state of emergency.

Red tides have been reported off the Florida coast since the 16th century, and they’ve probably been around for far longer. But four of the five longest-lasting red tides recorded in Florida have occurred in the past three decades, including the devastating 2018 bloom that killed some in tourism loss. “It is a naturally occurring process, but I think it’s intensified in recent years,” says Mark Rachal, Լ����Ƶ Florida’s coastal island sanctuaries manager. 

This year’s red tide is notable for both its severity and timing. Harmful algal blooms typically don’t appear until early fall and disperse by January. Experts say that it's unusual and troubling to see one so early in the season, when it can affect nesting birds and have plenty of time to intensify before the onset of cool weather.

Luckily, Short hasn’t yet seen any signs of red tide poisoning in the shorebirds she’s monitoring. She credits a shift in the birds’ diets. “We have been seeing many of the adults bringing freshwater fish to their chicks over the last couple of weeks,” she says. Regardless, she plans to keep a close eye on the birds, especially given the hundreds that perished during the 2018 red tide event. 

But not every bird population has gone unscathed. The Seaside Seabird Sanctuary has taken in more than 100 birds, including cormorants, gulls, pelicans, and herons, sickened by the toxin since June. They aren’t able to save them all, but they have rehabilitated most that come in. Many are back to full health and ready for release, says Melissa Edwards, avian hospital director for the Seaside Seabird Sanctuary in Indian Shores, Florida. But with the red tide intensifying, she says, “we just haven’t felt comfortable doing it yet.” 

Much like a hurricane, a harmful algal bloom’s severity is determined by a confluence of factors, says Barb Kirkpatrick, executive director of the Gulf of Mexico Coastal Ocean Observing System. This year, those included a perfect storm of pollution, drought conditions, strong winds, and ocean currents. 

Between March and April, the Piney Point fertilizer plant dumped more than 200 million gallons of nitrogen-rich runoff into Tampa Bay in order to prevent a leak at the facility from flooding the nearby community. Hundreds of residents were forced to temporarily evacuate over Easter weekend, and the incident drew outrage from environmental groups. Nitrogen is one of the key nutrients the toxic algae need to thrive. While this event did not directly cause the bloom, it almost certainly contributed to its severity, say both Kirkpatrick and Rachal. Winds and ocean currents from Tropical Storm Elsa also spread the microbes up and down Florida’s coast, where they combined with another burgeoning red tide event to the south. A warmer-than-average March and April could have also played a role in the early timing of this year’s bloom. In the coming decades, scientists worry that warming oceans could continue to make red tides longer and more frequent.

Like many harmful algal blooms in the Gulf, the Tampa Bay red tide is caused by a microscopic organism called Karenia brevis, which creates myriad concerns for coastal wildlife and people. When waves crash along a shoreline, the organisms break apart and release toxins, called brevetoxins, which can affect brain, nerve, and respiratory function in vertebrates. “They are very fragile,” says Centers for Disease Control environmental epidemiologist Lorraine Backer, who helps assess harmful algal blooms for the agency. 

In water and sea-foam, the toxin creates a hazardous soup. Exposed fish die quickly, their gills paralyzed. Consuming contaminated fish or shellfish can be dangerous for birds, dolphins, and terrestrial mammals, including humans. While shorebirds like skimmers and terns are most likely to be affected, wading birds are also vulnerable. They may lose their motor functions, and “almost appear drunk,” Edwards says.

Brevotoxins can also go airborne when bits of the organisms get trapped in tiny sea-spray bubbles. In this form, they pose a comparatively low risk to humans and terrestrial wildlife—but still drive people away from the beach. They might trigger allergy-like symptoms, such as watery eyes, runny nose, itchy throat, or, in more severe cases, difficulty breathing. “People with asthma may experience their symptoms for a longer time, even after they've left the beach,” says Backer. 

NOAA now monitors wind patterns and the concentration of these airborne particles across for its experimental Red Tide Respiratory Forecast, which currently has many beaches around Tampa Bay in the high-risk category. While Short does not consider herself to be sensitive to respiratory symptoms, this year, she’s suffered the effects firsthand. “It feels like you have a cold or something like that, but without actually having one,” she says, “I knew when I started feeling all of those symptoms that it was pretty bad.”