Red Tide Bloom Worsens In Southwest Florida

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A​ 100-mile-long bloom of red tide is floating off Southwest Florida, prompting warnings about respiratory irritation and potential fish kills on area beaches.

E​xperts say weather could be helping fuel the bloom, which first showed up in October after Hurricane Milton.

Low to moderate levels of Karenia brevis, the algae that causes red tide, were found in recent water samples from a​reas along the Gulf Coast from Manatee and Sarasota counties, through Lee and Collier counties and down to Monroe County in the Florida Keys.

High levels were found along one part of Sanibel Island, where health officials warned late last week of a high risk of respiratory irritation.

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Areas several miles off the coast of Naples also showed high concentrations of the algae.

D​rone images posted to social media showed the bloom lurking offshore in the Gulf of Mexico.

A neurotoxin in red tide algae can kill fish and other animals and cause respiratory irritation in humans. People with certain pre-existing conditions are especially susceptible.

H​ow Weather Plays A Role

Hurricanes can cause more runoff and stir up deep water, both rich in nutrients that scientists say can fuel algae blooms.

"Winds and currents transport the blooms," Eric Milbrandt, director of the Sanibel-Captiva Conservation Foundation Marine Lab, said in an email Monday. "Nutrient runoff from fertilizers (and) animal and human waste coming from the coastal rivers create favorable conditions near shore."

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Fish killed by the bloom at sea can also create more nutrients as they decompose. Milbrandt said the area is seeing some dead fish washing up on beaches, but not in large quantities. The bloom has mainly stayed offshore but can be blown closer by onshore winds, he said.

"The longer the bloom stays near the coast the more likely there will be stranded sea turtles, birds, and manatees as the toxin is consumed through the food web," Milbrandt said.

B​ecause conditions can change rapidly, it's important to check the daily forecast and Florida's red tide information page.

"Blooms are patchy and can impact some but not all areas," Milbrandt said. "Sometimes conditions the very next day are clear and OK."

S​outhwest Florida was hit by a devastating red tide in 2018.

Weather.com senior content writer Jan Childs covers breaking news and features related to weather, space, climate change, the environment and everything in between.