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Lake Okeechobee water is heading to Florida’s coasts. What that means for red tide

An aerial image from March 19 shows Lake Okeechobee water clashing with the Gulf of Mexico. The U.S. Army Corps of Engineers in February began releasing billions of gallons of lake water per day into the Caloosahatchee River.
Courtesy of Ralph Arwood and Calusa Waterkeeper
Tampa Bay Times
An aerial image from March 19 shows Lake Okeechobee water clashing with the Gulf of Mexico. The U.S. Army Corps of Engineers in February began releasing billions of gallons of lake water per day into the Caloosahatchee River.

The organism that causes red tide was found at trace levels in three counties last week.

It didn’t take long for the aerial images to emerge.

Just days after the U.S. Army Corps of Engineers said El Niño rains meant it needed to release Lake Okeechobee water into Florida estuaries, clean water advocates took to the sky to document the damage.

The images show plumes of murky lake water clashing with normally clear and sparkling waters. On the east coast, aerial imagery earlier this month showed lake water flowing out of the St. Lucie inlet and colliding with the Atlantic Ocean. On the west coast, the water poured out of the Caloosahatchee River and collided with the Gulf of Mexico.

The short-term consequences of Lake Okeechobee discharges are already becoming clear: In the St. Lucie River, salinity levels have dropped, putting oysters and other marine life at risk. If high volumes of lake water continue into April, oyster and fish spawning in the Caloosahatchee could be harmed, environmental nonprofits worry.

But what about the long-term consequences? What could continued Lake Okeechobee discharges mean for red tide on Florida’s Gulf Coast?

The general consensus among the state’s leading red tide scientists is that red tides, formed from colonies of seawater algae species, aren’t caused by freshwater Lake Okeechobee discharges. But the nutrient-rich discharges may be making red tide blooms worse.

The first thing to consider is the window when red tides are most common, said Kate Hubbard, director of the state’s Center for Red Tide Research.

Right now we’re outside of the time frame for when red tides historically flare up in late summer and into fall, Hubbard said. Karenia brevis, the organism that causes red tide, was detected at small “background” levels in three counties across Florida last week: Manatee, Bay and Miami-Dade. Harmful levels are considered 100,000 Karenia brevis cells or more per liter. For comparison, the levels found recently were less than 1,000 cells per liter.

“Red tide is challenging to predict, and it’s too soon to know if and how releases … might impact bloom formation later this year,” Hubbard said in an email. But also noteworthy: Harmful red tide bloom concentrations, as of the end of February, had not been detected offshore for the past eight months.

See the latest red tide water samples from the Florida Fish and Wildlife Conservation Commission here:

In 2022, Hubbard and a team of scientists at the University of South Florida and Mote Marine Laboratory published a paper examining the 2018 red tide bloom along the west coast of Florida — the worst bloom there in more than a decade.

Yonggang Liu, director of the university’s Ocean Circulation Lab and an author on the 2022 report, said it’s widely accepted that red tide blooms start offshore and are brought to Florida’s coastline by ocean currents. Once a bloom occurs near the coast — even if it’s at low concentrations — it could strengthen from Lake Okeechobee’s high-nutrient water.

But there are other factors that could hasten red tide in an area like Sanibel Island, which recent aerial photos suggest is seeing discolored water from lake releases. The coastline geometry of Sanibel could make it a red tide hot spot because it’s harder for offshore algae cells to flush out of the waterway, Liu said.

Bob Weisberg, a physical oceanographer at the University of South Florida, is hesitant to attribute red tide blooms to Lake Okeechobee discharges. But he noted that added nutrients from the discharges could help it grow.

“Curbing discharges might solve some other problems,” he wrote in an email, “like the blue-green algae that seems to be related to such discharges, but it is not a cure-all” for red tide.

When the Army Corps in February announced they would begin releasing fresh water to Florida’s coastlines, Lake Okeechobee sat at 16 feet, 4 inches above sea level. The feds blamed El Niño rainfall for a fuller-than-normal lake, which was bloated to nearly t2 feet higher in mid-February compared to a historical average spanning more than four decades.

More than a month since the corps began dumping lake water, it has dropped about 10 inches, according to the latest estimates.

As of March 18, the two-week average of water flowing out of the government-owned spillway in Alva had been in a range considered “damaging” for 29 days, according to a report prepared by the conservation nonprofit Sanibel-Captiva Conservation Foundation. The nonprofit is urging the corps to greatly reduce discharges by April 1, or if a red tide flares up off the coast of Lee County.

Over the past week, a wildlife hospital on Sanibel had admitted an adult and a juvenile laughing gull with suspected toxicosis from red tide, or possible exposure to the algal toxins found in the water, according to the nonprofit’s report.

Over the long-term record, there’s “consistent evidence” that Lake Okeechobee discharges are making red tides worse or enabling them to last longer, according to David Kaplan, an associate professor at the University of Florida who, in 2022, helped co-author a study about the connection between lake releases and red tides. Right now, it’s important to monitor the red tide conditions offshore, he said.

The longer discharges happen, the more time red-tide-causing algae species have to intercept lake water coming from the center of the state, Kaplan said. Short-term releases of lake water have less of an effect.

Knowing that, the feds will start a two-week rest period on Friday, halting discharges to give both estuaries a chance to rebound their salinity levels and “catch their breath,” according to corps spokesperson Jeffrey Prater.

“I don’t have a crystal ball or a telephone line to the Corps, but there’s going to have to be releases to get the lake where it needs to be,” Kaplan said.

“We’ll be watching closely.”

This story was produced in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative formed to cover the impacts of climate change in the state.  

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Max Chesnes | Tampa Bay Times