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Hotter Temperatures Made for a Super Slimy Season

Lake Okeechobee was inundated with algae this summer, in part due to fertilizer runoff. Record-breaking temperatures and hurricanes may further exacerbate the lake's algal bloom problem.

Nathalie Vega

Sep 25, 2023

Intense heat battered Floridians this summer like never before. The Northern Hemisphere experienced its warmest summer on record. Combined with hurricane season, the intense heat brought algae blooms back to Lake Okeechobee with a vengence, staining its deep blue waters with various shades of green slime.

Hurricanes in Florida can cause phosphorus-rich fertilizer runoff to enter the state’s waters. They can also stir the bottom of the lake’s pollution and possibly harm the environment. These factors can promote algae growth every year, but the high temperatures can increase the severity of harmful algal blooms (HABs) in the lake.


On Sept. 11, the Florida Department of Health in Palm Beach County even issued a health alert due to HAB toxins in two of the lake’s locations, and advised residents and visitors to avoid coming into contact with waters where there are visible blooms.

Throughout this summer, lime-green swirls of slimy algae coated many parts of the lake, carrying a strong odor of fish and rotten eggs to shore.

According to Larry Brand, a professor at the University of Miami’s Rosenstiel School of Marine, Atmospheric, and Earth Science, Lake Okeechobee has one of the worst algal bloom problems of any body of water in Florida.

Lake Okeechobee’s blue-green algae, also known as cyanobacteria, produce toxins that can lead to liver cancer and neurodegenerative diseases such as Alzheimer’s, said Brand.

HABs have produced fumes and poisons that can kill animals who play in the lake’s slimy waters, and they can even cause health problems in people who inhale the toxins.

The toxins from the algae can move up the food chain, and if people are using that polluted water to irrigate their crops, the toxins can end up in the crops, Brand added.

Brand explained algal blooms are likely to form where there is a lot of urban development and agriculture. He said the blooms are found where there are excess nutrients.

According to the St. Johns River Water Management District, nutrient pollution refers to “an overabundance of the essential plant nutrients nitrogen and phosphorus.”

Those nutrients enter the water from sources such as stormwater runoff and can trigger algal blooms in the right conditions.

A frog pokes his head up in the middle of a thick layer of algae (Michela Lommi on Unsplash)

“Usually the dominant sources are runoff of either fertilizer from agriculture or sewage,” Brand said.

Lake Okeechobee’s harmful cyanobacteria are more likely to bloom when there is warm, sunny weather and when there is high rainfall. 

When toxins accumulate in the food web, they can cause health problems in people who consume certain fish, according to Edward Phlips, a professor of algal physiology and ecology at the University of Florida’s School of Forest, Fisheries, & Geomatics Sciences.

According to Phlips, there are hundreds of species of algae in Lake Okeechobee, but cyanobacteria often dominate the lake when algae concentrations are high.

Phlips said some species of cyanobacteria can produce toxins, which in turn can lead to gastrointestinal issues and liver damage. Moreover, he said, respiratory symptoms are typically associated with neurotoxins like saxitoxin and anatoxin. Neurotoxins’ main symptoms are respiratory distress and eye irritation. This can affect humans if the neurotoxins become aerosolized, or turned into fine solid or liquid particles suspended in gas.

He also explained algal blooms can be affected by light availability. Some areas can have nutrients without many algal blooms due to insufficient light. Temperature can also affect the blooms’ rate of growth.

“There is less probability of having a bloom in the winter than in the summer because of the low light availability and the low temperatures, which can reduce the growth rates to the point where a bloom is less likely,” Phlips said.

According to the U.S. Environmental Protection Agency, warmer temperatures prevent water from mixing, allowing for faster and thicker algal growth. When blooms absorb sunlight, it warms the water and promotes more blooms.

Phlips said blooms can also create oxygen-deficient conditions and this can lead to an ecosystem-disruptive phenomenon that includes the mass mortality of fish, invertebrates, and other parts of the food web. 

However, despite these potential consequences, the scientific community does not fully agree on the causes of these blooms.

According to Daniel Canfield Jr., a professor of Limnology at University of Florida, the idea that warmer temperatures promote more algal blooms is a hypothesis, and there is no documentation of it.

Canfield said in an interview that these algal blooms are becoming more recognized because social media allows people to see them.

“The frequency is due to the fact that people are looking for them and reporting it,” Canfield said.

According to Canfield, the algal blooms in the lake cannot be stopped.

“Some people want it to be crystal clear,” he said. “It never was that, and never will be that.”

Florida has taken some steps to clean up the state’s waters, however. In April Gov. Ron DeSantis announced an award of over $13.6 million for innovative technologies and short-term solutions to help prevent, clean up and mitigate HABs.

According to Duane De Freese, the Executive Director of the Indian River Lagoon Council (IRL), a special district of Florida, DeSantis and the state of Florida have appropriated historic levels of funding to address HABs by tracking and addressing nutrient reduction. They have done this by improving water quality through improvements in wastewater, septic tanks, and stormwater.

De Freese explained that federal agencies like the National Oceanic and Atmospheric Administration (NOAA), universities working on algal bloom dynamics, and scientists are all looking at the conditions that initiate, sustain and terminate blooms by monitoring them and making models to better predict these conditions.

“Florida has taken its leadership role over the last few years to address those infrastructure issues,” De Freese said. “We have a long way to go, though.”

According to De Freese, the biggest challenge in addressing algal blooms is public awareness that the problem can be mitigated  with adequate public and private funds to help solve the problem.

“There’s no question that additional funding is needed for monitoring, for science, but without public support to address this issue, you can’t get there,” said De Freese.

De Freese explained HABs impact their surroundings while the bloom is growing and when it is terminated. He also said these blooms consume oxygen when they die, killing fish and other sea creatures.

That is why the blooms are monitored every time a hurricane hits Florida. In fact, last year’s Hurricane Ian churned up Lake Okeechobee, worsening a blue-green algae outbreak. With more than two months left of hurricane season, experts are worried that the algal blooms could worsen.

This story was produced by MediaLab@FAU, a project of Florida Atlantic University's School of Communication and Multimedia Studies. If you would like to republish this article, please credit the writer and MediaLab@FAU. The reporter can be reached at

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