Just before Hurricane Michael made landfall last month, a ferocious red tide that had scoured Florida’s Gulf Coast for a year, depositing countless dead sea turtles, dolphin and other marine life on beaches before spreading to the Atlantic coast, had finally started to wane.

In most places, with the wet season winding down and the U.S. Army Corps of Engineers easing up on releasing polluted water from Lake Okeechobee, the toxic algae that had become a key election year campaign issue had dropped to relatively low levels. Fish kills were down and so were the coughing fits among beach-goers.

But in the weeks following the storm, red tide that is already considered the worst in a decade has roared back.

Click to resize

On Monday, state wildlife officials logged high to medium levels along beaches from Clearwater to waters off Everglades City and in the Panhandle. Fish kills were reported in nine counties from the Panhandle around the tip of the state to the Space Coast. Along the Atlantic coast, levels capable of killing fish and causing respiratory distress remained along Cocoa Beach and in Martin County, but had dropped from Friday to Monday along other stretches of the Treasure Coast.

Red tide caused widespread fish kills on Florida’s Gulf Coast beaches this summer, including this one on Sanibel. Getty Images

Why that is remains a little bit of mystery. Red tides have many factors at play, and remain tricky to predict. But it’s likely a combination of wind, pollution and the tiny algae that cause the blooms, one of the few with the ability to swim, conspired to revive the tide.

“I kept hearing this argument, ‘Yeah, let’s bring a hurricane and that’ll flush everything out.’ But not necessarily,” said Nick Shay, an oceanographer at the University of Miami Rosenstiel School of Marine and Atmospheric Science.

While hurricanes can mix up the ocean and sometimes even provide a healthy flush — following Hurricane Irma guides in the Key and Ten Thousands Islands happily reported a surge in fish — red tides require more than a one-time flush. Polluted run-off from a storm’s heavy rain or retreating storm surge also likely provide the blooms with an injection of fuel.





As Michael crossed the Gulf as a fierce Category 4 storm, Shay said temperature data show heavy mixing occurred across the long steep slope of the Florida Shelf where the red tide algae, Karenia brevis, live. Water from the shelf was then pushed ashore as Michael passed to the right, he said.





As Hurricane Michael crossed the Gulf of Mexico last month, it stirred up water as this temperature map reveals, cooling waters by 4.5 to 5.4 °F, and likely churning up the bottom-dwelling algae, amplifying the problem. Source: Jodi Brewster, University of Miami Rosenstiel School of Marine and Atmospheric Science.

Michael, Shay said, in effect did the opposite of Hurricane Irma, which occurred in September 2017 a month before Mote Marine Laboratory scientists first detected red tide off Sarasota in October, and he suspects helped trigger the current bloom: As it slid up the coast, Irma sucked water off the coast and sent algae-laden water from the bottom ashore.





“It’s still essentially the same recipe,” he said.

For the tide to be flushed out, National Oceanic and Atmospheric Administration oceanographer Rick Stumpf, who monitors harmful blooms, said regular seasonal fronts need to arrive. The fronts carry northerly winds that produce a southbound current which can help push the tide offshore. That’s typically what happens, and what failed to happen last January and February when winds were remained to mild, he said.

“We had this nondescript, probably gorgeous weather and the wind not going in any direction,” he said.

As seasonal winds pick up, Stumpf said there’s also a chance other algae that live in the Gulf and do better in windy conditions— the good algae that don’t carry toxins and form the basis of the food chain — could begin to thrive. Those algae can’t swim and tend to sink in calm weather while the tiny swimming Karenia brevis fare better in calm water. With the wind, the good algae remain suspended, feed off nutrients and out-compete the red tide algae, he said.

“It’s not the shear amount of the wind. It’s the frequency of the wind,” he said.

Source: National Oceanic and Atmospheric Administration.

Tides in the Gulf are a seasonal event, arriving in late summer or early fall and usually last three to five months, state scientists say. That’s because a permanent population of Karenia brevis live on the bottom of the Florida Shelf. But after the tide first appeared, it wafted up and down the coast for months and never subsided. Over the summer as the rainy season deepened and the Corps began releasing polluted water down the Caloosahatchee River to ease pressure on the aging dike around Lake Okeechobee, the tide exploded in Pine Island Sound, littering beaches with tons of dead fish. Nutrients in pollution, especially in fertilizer, can feed the nutrients, so scientists suspect the lake releases worsened the problem.

“The pure chemist would say we haven’t proven it. We need lots more data. But it seems pretty evident to me. It’s nutrient laden. That’s why we have blue green algae,” said Florida International University coastal ecologist Steve Leatherman.

The tide was then carried down and around the coast by the Florida Current and up the Atlantic coast, where tides rarely occur. The appearance of the tide in Miami-Dade in low amounts marked the first time since !972 when the New York Times reported an incident, according to Rosenstiel researchers.

The massive fish kills on the Gulf Coast closed beaches and generated gruesome images of dead sea turtles, dolphins, tarpon. redfish and mounds of bait fish that made national headlines. It also drew attention to Gov. Rick Scott’s environmental record, which included slashing budgets for agencies that manage and monitor water and enforce pollution regulations. Scott, who is in a heated race with Sen. Bill Nelson for a seat he has held for 18 years, has declared a state of emergency and poured $20 million, mostly for clean-up and to boost tourism, into addressing the crisis.

A Kemp’s Ridley sea turtle was among the numerous dolphins, manatees and other marine life around the Florida coast killed by red tide poisoning. Photo by Andrew West/News-Press Andrew West The News-Press

Yet the tide is continuing to take a toll, especially on waterfront businesses. Waitresses and waiters are earning a fraction of their regular take-home, the Tampa Bay Times reported Friday, and hotels continue to see a drop in bookings.

While the red tide bloom on the Atlantic Coast has been less intense, the high numbers are still worrisome, said Rosenstiel algae expert Larry Brand. Usually counts remain low because the algae are dispersed as they are carried hundreds of miles by the Florida Current. High numbers suggest the algae could be beginning to multiply as well.

“The fact we’ve had high concentrations up there suggests it’s growing. It’s not just getting carried over, but it’s growing. It’s surviving off the nutrients coming off land,” he said.

The drop in numbers in some locations over the weekend could stem from a quick front that moved through. It’s also possible that eddies that form in the shifting Florida Current trap the algae as they do with other chemicals like oil and other debris, Shay said.

Going forward, scientists are hoping to come up with better ways to forecast the tide. Stumpf said he is working with the University of Florida-based Sea Grant on to put together a satellite imagery showing how the bloom evolved over the summer. The work should be ready in a week.

“We can forecast the past with great accuracy,” he joked. “The question is can we turn that around and actively forecast the future and we have not had success in trying to forecast [red tide] blooms so far.”