Red tide persisting along Southwest Florida coast

Red tide is still plaguing coastal areas in Collier and Lee counties, but the outbreak is patchy and weaker than it was a few weeks ago. 

The Florida Fish and Wildlife Conservation Commission reports varying conditions in the region, with counts ranging from natural background levels to 1 million cells per liter and higher. 

Respiratory irritation was reported this week in Collier, Lee, Manatee, Pinellas and Sarasota counties. 

"We had respiratory irritation reported at all of our beaches (Tuesday) due to the onshore winds," said Rhonda Watkins, an environmental specialist with Collier County Pollution Control. "There have been no reports of dead fish this week."

Most recent counts show low to medium concentrations along the Southwest coast, although there is a spike in the Captiva area. 

Conditions for beachgoers and boaters depend on whether the wind is blowing onshore or offshore.

Onshore winds bring airborne red tide particles to coastal areas while offshore winds push the toxins out into the open Gulf of Mexico. 

Winds have been mostly onshore in recent days. 

The National Weather Service says winds here will be out of the northeast or southeast through the rest of the week, which is good news for those affected by red tide. 

On Wednesday afternoon "winds will shift to the northeast and will remain offshore through Saturday, so this should help minimize any impacts at the beaches," Watkins said. 

This bloom (caused by the organism Karenia brevis) was first documented by the National Oceanic and Atmospheric Administration in October 2017 and is the longest outbreak in more than a decade. 

It's been patchy in Collier and Lee in recent weeks, showing up on certain beaches one day and disappearing the next. 

"Monday was the first day we started feeling the effects of it, and Tuesday the winds were coming onshore, but (Wednesday) we felt nothing," said Thaddeus Kassab, with Marco Island Water Sports. 

Kassab said the water looks like it would during any cold front — wavy and churned up. 

"But we haven’t seen any red tide, and one thing we haven’t seen in Marco is dead fish on the beach," Kassab said. 

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Millions of pounds of dead fish and marine wildlife were collected on Lee County beaches in a few weeks this summer when the red tide outbreak was at its worst. 

Hundreds of sea turtles, dozens of dolphins and even a whale shark are thought to have been killed by red tide since July. 

Nearly 40 dolphins have washed up on Collier and Lee beaches in the past two weeks, and red tide is suspected in those deaths. 

An increased number of coastal bird species have been brought to the Center for the Rehabilitation of Wildlife on Sanibel, the center reports.

The Conservancy of Southwest Florida in Naples also has been treating an increased number of coastal birds and animals. 

Red tide counts this summer were well above 1 million cells per liter, the highest number the FWC reports for a water sample. 

Some measurements this summer were 100 million cells per liter and higher, Rick Bartleson, a water quality scientist with the Sanibel-Captiva Conservation Foundation, and others have reported. 

Satellite imagery shows high levels of chlorophyll A offshore Collier and Lee, which is likely a larger, more dense area of red tide, Bartelson said. 

Those denser conditions may be what caused the dolphin and whale shark deaths. Toxicology tests have been or will be conducted on those animals, although an exact cause of death is likely to remain unknown. 

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Cold weather fronts are key to getting rid of a red tide bloom.

Blooms typically start in October or November and end in January or February, although some outbreaks have lasted a year or more. 

The University of South Florida's College of Marine Science predicts that the surface of the bloom will move to the southwest over the next three days. 

It may take several cold fronts to squash this outbreak, which has caused massive fish and marine wildlife kills over the past five months. 

Cooler water temperatures that come with the cold fronts hinder algae growth. 

"The wind is probably more important," Bartleson said. "If we have enough sustained cold fronts that will keep the patches from being able to maintain these high densities. It spreads them out. But it’s hard to get rid of with one cold front. You need to keep them coming."

Connect with this reporter: Chad GillisNP on Twitter.