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Florida’s coastline is being littered with dead fish as algal blooms once again turn the water a toxic reddish-brown color. While this “red tide” is a regular occurrence in parts of Florida and Texas (as well as nearby coasts of Mexico) in the summer and fall, scientists say the algae has arrived earlier than usual and at higher-than-normal levels.

The algae responsible for red tide is Karenia brevis, a microscopic, single-celled organism that produces potent neurotoxins called brevetoxins, which can cause large die-offs of marine organisms and seabirds. It also poses risks to human health, such as skin irritation and breathing problems. Brevetoxins can also accumulate in shellfish like clams and oysters, potentially causing food poisoning when consumed.

Over the past few days, Fort Myers Beach, which is around seven miles long, has seen more than 13 tons of dead fish wash up. On the beaches of Siesta Key, off the coast of Sarasota, hundreds of dead fish have washed up along miles of coastline, with beachgoers experiencing burning eyes and frequent coughing. According to Matthew Garrett, a biologist at Florida’s Fish and Wildlife Research Institute, potentially harmful concentrations of the algae have been detected in the waters along about 150 miles of the state’s Gulf Coast, with the bloom extending between 3 and 10 miles out to sea.

While red tide is a natural phenomenon, scientists say climate change is worsening the problem. K. brevis thrives in water temperatures up to about 83 degrees, but it doesn’t grow as quickly beyond that. However, researchers have discovered that the algae can tolerate higher temperatures and grow faster given increased levels of carbon dioxide—the primary greenhouse gas emitted through human activities.

Killing or even controlling the algal blooms has proven to be almost impossible, so the severity of the early red tide doesn’t bode well. Flordians can only hope that it doesn’t get as bad as 2017–2018, when some 2,000 tonnes of marine life perished, including hundreds of turtles, dozens of manatees, and even a whale shark.

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