Red tide appears to be declining off south Lee, Collier counties

Chad Gillis | The News-Press

Show Caption Hide Caption Very high counts of red tide found in patches off of Sanibel Island according to researchers Very high counts of red tide found in patches off of Sanibel Island according to researchers

A red tide bloom that's lingered along the coast for several weeks may be waning as counts in south Lee and parts of Collier County have improved in the past week.

Reports from the Sanibel area south to Marco Island show that the outbreak appears to be subsiding, which would be a welcome reprieve from an area that's seen red tide in all but seven months out of the last two-plus years.

"Counts appear to still be elevated, but patchy, varying from beach to beach," said Rhonda Watkins, an environmental specialist with Collier County. "However, it appears on the most recent satellite imagery that the entire bloom has dissipated, so fingers crossed, that trend continues."

Fish kills and breathing irritation can start once levels reach 10,000 cells per liter, according to the Florida Fish and Wildlife Conservation Commission, the state agency that monitors red tide.

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FWC's Friday report was not available at press time.

"We had quite a few dead fish at our north Naples beaches and some on Marco (Monday)," Watkins said. "We are getting respiratory irritation reports whenever the wind is blowing onshore."

Levels this year have upwards of 15 million cells per liter and higher, according to samples taken by local water quality scientists.

The bloom is strong enough to show up on satellite imagery from the National Oceanic and Atmospheric Administration, or NOAA.

Recent satellite images have shown clearer patches of water along the Southwest Florida coast, although there are areas where red tide levels are still high.

Red tide is caused by the organism Karenia brevis and is naturally occurring in the Gulf of Mexico, although many water quality scientists say it can be fed by human-sourced nutrients when the blooms get close to shore.

Relatively small fish kills have been reported in Lee, Collier and Charlotte counties for several weeks.

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Rick Bartleson, a chemist with the Sanibel-Captiva Conservation Foundation, said samples he's taken this week have improved and that some waters off Sanibel are actually clear and blue.

"It looks like the big patch that’s been hanging off the south end of the Sanibel for weeks is about gone, and from our samples since Monday we haven’t seen any high levels," Bartleson said.

This outbreak is more of a "normal" bloom than the one that devastated the region between October 2017 and earlier this year.

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That bloom killed millions of pounds of marine life and shut down the local tourism, real estate and recreational fishing industries.

"This year continues to be a fairly normal year when you look at the cell numbers and where we’re seeing the high concentrations," said Mike Parsons, Florida Gulf Coast University professor and Blue-Green Algae Task Force member. "They’re at about the same frequency we usually see."

Water quality scientists at the University of Miami say red tide blooms are more frequent, stronger and longer in duration than they were before modern development, farming and urbanization of coastal areas.

Onshore winds push red tide blooms toward the coast, and offshore winds push any outbreak further into the Gulf of Mexico.

Winds have been blowing out of the east, or offshore, in recent days, and that trend is expected to continue much of this week, according to the National Weather Service in Ruskin.

The bloom seems to have started south of the Naples area in late summer/early fall and is now centered around Lee waters.

Strong counts of 1 million cells per liter and higher have been recorded in the northern reaches of Pine Island Sound for several weeks.

"The (daily incoming) tide will be moving the water in, and we don’t necessarily have the outflow because we don’t have a lot of freshwater discharge (from the Peace River and its watershed)," Parsons said. "So once it gets into Pine Island Sound the wind can't push it around."

The University of South Florida's College of Marine Science predicts that the bloom will drift southwest and away from the coast over the next three days.

Connect with this reporter: @ChadGillisNP on Twitter.