What’s an algae bloom and how did it wind up sliming Florida’s biggest lake?

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Algae is one of the planet’s basic building blocks, living and growing in nearly every body of water to feed the cycle of life. Blue-green algae, the stuff now grabbing headlines across Florida, is among them, with hundreds of algae species filling the state’s lakes.

But add pollution — the phosphorus and nitrogen from farm fields and leaky septic tanks — and good turns to bad, fueling explosive blooms. When things get really rough, toxic subspecies appear that can cause liver and brain disease.

Over the last month, blue-green blooms have spread across Lake Okeechobee, igniting a crisis as they quickly moved from a shallow, moon-shaped wedge in the southwest corner that scientists call the “fertile crescent” for its ability to produce blooms. By last week, as water circulated counterclockwise, 90 percent of the 370-square-mile lake was filled with foul green slime. Smelly water looking like a rancid smoothie also flowed down the Caloosahatchee River toward the southwest coast. In some areas, two toxic subspecies of the algae were detected.

The Treasure Coast on the east side of the state is now bracing for the same, with the U.S. Army Corps of Engineers expected to open gates in the coming days as part of its regular wet season plan to keep lake levels down and protect the lake’s aging dike.


Calusa Waterkeeper John Cassani collects a sample of blue-green algae from the Caloosahatchee River west of LaBelle in late June. Blooms started filling the river in late June after they appeared in Lake Okeechobee earlier in the month.

Pedro Portal pportal@miamiherald.com

So why did the lake explode now and how long will the blooms last? Blue-green algae, or cyanobacteria, is complicated, with each bloom having its own characteristics.

But Karl Havens, director of Florida Sea Grant and a University of Florida biologist specializing in water pollution, said blooms follow a basic recipe: pollution, sunlight and warm water. In other words, Florida.

“You can write stories like this for 50 years,” he said. “Every year, with a lot of rain and the hot summer, it’s going to be like this.”

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Levels of pollution and water temperature are the key drivers, with elevations of each spurring growth, said Tim Davis, a Bowling Green State University microbiologist who studies blooms in Lake Erie.

After Hurricane Irma stirred up pollution and killed off vegetation in the sunny fertile crescent, the stage was likely set. Record-breaking rain in May provided an extra dose of pollution. Sunny, calm days in June pulled the trigger.

Lake O became a breeding ground over the decades, as farm fields and towns appeared around the lake and filled it with phosphorus and nitrogen. Cyanobacteria thrive on such pollution, so they tend to muscle out the competition and take over.

“Conservatively, the doubling rate is two days,” Davis said. “And then the rate is exponential.”

While it’s not clear why, toxic subspecies can sometimes start to grow, Havens said. Three commonly appear in Florida: microcystis, anabaena and cylindrospermopsis. But they don’t always release their toxins, at least not immediately.

“It’s not completely understood,” he said. “Sometimes a large microcystin bloom could have toxins but not release them until it collapses.”

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A bottle of water collected from the Caloosahatchee River west of LaBelle in late June is filled with foul smelling algae.

Jenny Staletovich jstaletovich@miamiherald.com

Getting rid of the pollution would obviously solve the problem. But that’s complicated in Florida. In the 1980s, the state ordered dairy farms to contain the waste from their cows. In 2009, sugar growers to the south curtailed decades of back-pumping water loaded with fertilizer from fields. But the wetlands and creek beds to the north that drain into the lake are still filled with nutrients that flow into the lake, Havens said. The South Florida Water Management District is in the midst of building projects to hold and clean the water. But mud at the bottom of the lake is also laden with phosphorus and nitrogen, he said.

“If you stopped the sources tomorrow and everything went to zero, there’s enough stuff in the old pollution that it would take another 50 years to go away,” he said. “Then on the bottom of the lake, you have mud that contains a huge amount and every time the wind blows it stirs it up.”

The Everglades Foundation has launched a $10 million competition to find an answer. Later this year, four final teams will try to solve the pollution problems killing Lake Jesup, one of Central Florida’s sickest lakes, as a trial run.

But Havens said Lake O holds at least 500 million cubic yards of polluted mud, which is also tainted with toxic metals.

“If every dredging boat in the world worked for 20 years, they couldn’t move it,” he said.

Blooms in the Caloosahatchee and St. Lucie estuary are also fed runoff from the surrounding land, he said. So just cleaning up the lake won’t necessarily stop blooms on the coast.

How long the blooms will last is uncertain. Davis said other things sometimes hurt blooms: Viruses can attack them or they run out of nutrients. But usually if temperatures remain high, they persist. Cloudy days could block sunlight and kill them. Heavy rains or a storm during hurricane season could also flush them, Havens said. Blooms appeared in 2004 after Hurricanes Frances and Jeanne plowed across the state, but then got flushed by Wilma the following year, he said. Cooler temperatures in the fall could also wipe them out.

“But it might not,” he said. “It’s a bad situation because what we’re talking about here is such a high level of nutrients.”

That’s why controlling pollution becomes the deciding factor in addressing blooms, he said. Another looming risk is climate change. Scientists have documented a warming trend in lake water temperature over the last 25 years linked to a hotter planet. That means blue-green blooms could become more frequent and worse if no change is made to the amount of pollution.

“There’s such a high level of nutrients in the lake that weather now determines if you have algae blooms,” he said. “So the thing you can’t control determines whether there’s a bloom or not.”

Follow Jenny Staletovich on Twitter @jenstaletovich

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