Algal blooms in Florida’s waters have become an increasingly consequential challenge—here’s what you need to know.
Slimy, scummy, ninja-turtle green cyanobacteria. Water staining, breath-stopping red tide blooms. Brown, spider-web growth and muck that smothers beneficial seagrasses.
At varying degrees, when these blooms grow beyond balanced levels, they’re all bad for the health of our waters and water-based economy. Some can have toxic, directly lethal impacts while others slowly lead to environmental destruction by upsetting the natural order in the system, but they all threaten clean water.
And unfortunately, with temperatures heating up and the official start of the rainy season in the rear-view, the potential for widespread blooms is on the rise. So, what exactly are algal blooms? Why are they a threat? What makes some more dangerous than others? And most importantly, what causes them, why have they been getting worse, and how can we mitigate them?
What are algal blooms?
Algae is actually a fundamental part of a waterbody, but that’s only if it’s present in natural, balanced amounts. These plant-like organisms are at the foundation of the marine food chain, and they can help oxygenate the water.
But algae can easily grow out of control, creating what’s called a bloom. When this happens, algae’s role in the ecosystem seemingly shifts from one of beneficial contributor to parasitic threat, adopting “take all, leave nothing” behavior.
If the conditions are right, their growth can go unchecked, and whatever is in their path will likely feel it in one way or another.
What’s the threat?
The most dangerous types of algal blooms are Harmful Algal Blooms (HABs). According to the National Oceanic and Atmospheric Administration (NOAA), HABs occur when colonies of algae “grow out of control and produce toxic or harmful effects on people, fish, shellfish, marine mammals and birds.”
The two major HABs that plague Florida’s waters are Red Tide and Blue-Green Algae, both of which come with a laundry list of problems.
Red Tide
Red tide is caused by a marine dinoflagellate known as Karenia brevis. Blooms form offshore in the Gulf of Mexico, but when conditions are right, they can be moved onshore by upwellings, posing a toxic threat to coastal environments.
“What’s important to note about red tide is that it does produce a neurotoxin that can impact fish, wildlife, and even humans to some degree,” explains James Evans, CEO of Sanibel-Captiva Conservation Foundation, a non-profit that carries out red tide and other water-quality monitoring programs in southwest Florida. When airborne, that neurotoxin—called brevetoxin—can cause respiratory illness and eye irritation in humans.
The effects on marine life are even more severe. Supercharged red tide blooms—like those experienced most recently in 2021, 2018, and 2016—can kill thousands of tons of fish, turtles, dolphins, birds, and marine mammals. Wildlife either succumbs directly to the brevetoxin, or they perish as a result of the low-oxygen, dead zone that’s created by the decaying of other dead fish and red tide cells.
Photo courtesy of Capt. Dustin Pack, Tampa Bay Waterkeeper
Last year, a major red tide event littered the banks of Tampa Bay with dead dolphins and fish, including a couple of half-grand goliath groupers. During the water crisis in 2018, a whale shark washed up on the shores of Sanibel Island, shocking beachgoers.
That dent to our wildlife is bad enough, but it also creates additional health hazards and requires extensive, expensive clean-up for the community, all of which affects local real estate and water-based businesses like hotels, restaurants, fishing guides, and more. “It’s really a harmful algal bloom for a number of reasons,” notes Evans. “It’s harmful to the fish and wildlife, but it’s also harmful to human health, and it’s harmful to our economy.”
Blue-Green Algae
Often neon green in color, toxic blue-green algae blooms (technically a type of photosynthetic bacteria known as cyanobacteria) can stack up in stagnant water and create out-of-this-world scenes. The consequences of blue-green algae are similar to those of red tide, but they most directly affect fresh and brackish waterbodies—where they form—rather than saltwater or estuarine environments.
The most common species found in Lake Okeechobee and the St. Lucie and Caloosahatchee rivers is Microsystis, which produces microsystin, a potent liver toxin and possible human carcinogen.
These toxins can be absorbed through ingestion, direct contact, or by breathing in contaminated air. Research has shown cyanobacteria particles aerosolize and travel miles from blooms, which in Lake Okeechobee can regularly reach concentrations that surpass the EPA’s “safe for human contact” threshold by over 100 times.
Pets have died from drinking contaminated water, and humans can experience acute symptoms like rashes, stomach cramps, nausea, diarrhea, vomiting, and respiratory irritation. Because the long-term effects of blue-green algae on humans are not widely understood, they have become the focus of recent research efforts, like this ongoing study by the University of Miami.
Economic Impacts of HABs
Needless to say, the threats posed by a severe red tide bloom or blue-green algae outbreak can easily turn affected waterways or beaches into no-go zones. They can effectively shut down entire water-based communities, and in Florida’s tourism-fueled economy, that can be devastating.
In a 2020 report, the University of Florida investigated the economic impacts of the 2018 water crisis. Using survey results and Airbnb reservation statistics, the study estimated that event led to $184 million in direct losses to the tourism industry in Florida. It also found that charter/for-hire businesses averaged a 61% decrease in revenue when red tide was present in their areas.
But that’s just the tip of the iceberg, and it’s only the initial wave of damage that algal blooms can incur. There are longer-term, more subtle impacts working beneath the surface too.
Indirect effects of algal blooms
The widespread overabundance of algae in Florida’s waters (beyond just red tide and blue-green algae) can have cascading effects on our marine ecosystems. It’s not just the direct poisoning, it’s also the loss of critical habitat—like seagrasses—that can put the casualty count over the top.
When certain types of marine algae grow beyond natural levels, it can throw off an ecosystem in a number of ways. We already mentioned the oxygen depletion caused by decomposing red tide, which leads to dead zones in the water and secondary fish kills, but some algae can grow so thick, they kill other life-sustaining aquatic vegetation too.
Essentially, when some blooms grow out of control, they block sunlight from reaching other vegetation—like seagrasses—preventing photosynthesis and killing the plant. That’s been the peril of the Indian River Lagoon over the past decade, where repeated harmful algal blooms have led to the loss of more than half of all the seagrass found in the 150-mile east-coast estuary.
Now, the lagoon is struggling to support the biodiversity that’s earned it federal recognition as an Estuary of National Significance, and the loss of seagrass has taken a hit on the entire food chain. “That loss of seagrass and those water quality problems are impacting our biological resources all the way up the food chain, including manatees and our fisheries,” says Duane De Freese, Executive Director of the IRL Council and the Indian River Lagoon National Estuary Program.
Baitfish, shrimp, and crabs have nowhere to hide; game fish have nowhere to chase bait; and treasured species like manatees have lost their primary forage. The situation is a sure crisis—one that’s spiked manatee deaths to record levels and instigated hail-Mary projects like this one that desperately resorts to feeding Florida’s gentle giants with lettuce.
Similarly on the west coast, we’re seeing mass swaths of drift algae replacing seagrasses at an act-now-or-regret-it-later rate. Giant rafts of brown algae known as Lyngbya clutter up Charlotte Harbor’s eastern shores, looking and smelling like a sewage treatment plant. Former seagrass flats are now barren expanses or covered in green algae.
Turtle Grass and Shoal Grass are getting harder and harder to find. In fact, according to the South Florida Water Management District, Charlotte Harbor lost 23% of its seagrasses between 2018 and 2021—that’s 4,500 acres, which represents 30 years of recovery growth.
The worst part is, seagrasses help stabilize and clean our waters, so when we lose them, the cycle is perpetuated. And unfortunately, the problem isn’t limited to the Indian River Lagoon and Charlotte Harbor, we’re seeing it all over the state.
How did we get here?
So, what’s causing these out-of-control events, and how do we mitigate them?
Like other plants, these algae use sunlight, water, and nutrients to grow. Right now, Florida’s waters are heavily polluted with excess nutrients, like nitrogen and phosphorus, and they’re fueling these blooms to unprecedented levels.
Under normal conditions, nutrient levels in an aquatic ecosystem support a balanced growth of grasses, algae, and other marine life. However, when land-based activities introduce excess nutrients into the system, fast-growing algae, like red tide and blue-green algae, have a competitive advantage.
That’s what has been plaguing Florida for years. Nutrient pollution from a variety of sources like stormwater runoff, sewage spills, faulty septic tanks, old phosphate mines, agriculture, and Lake Okeechobee discharges create an environment prime for algal growth.
And although that cause-and-effect relationship has been assumed for many years, it took until very recently to confirm it with scientific evidence. However, a new study published by the University of Florida has directly linked manmade nutrient pollution, like the nitrogen-laden high-volume Lake Okeechobee discharges, to intensifying red tide blooms.
The study, spearheaded by UF’s Center for Coastal Solutions, concluded that “nitrogen-enriched Caloosahatchee River discharges have consistently intensified K. brevis [Red Tide] blooms to varying degrees over time.” Simply stated, the nutrient-rich discharges make red tide blooms worse.
What do we do about it?
Many municipalities will implement their annual fertilizer bans within the next few days, usually kicking off around June 1st every year and continuing through the wet season. That ban is intended to keep rainfall from washing nutrients in lawn fertilizers into our waters, which is great, but it’s only a small fraction of the problem.
There are many other, larger contributors and polluters that individual citizens have much less—if any—direct control over. Ultimately, it’s up to the state to create and strictly enforce more meaningful policy to prevent all nutrient pollution from entering our waters. Thankfully, that’s where the people can influence the situation by using their voice to create the pressure for change.
Demand that your city or county prioritize strategies, techniques, and upgraded infrastructure to prevent nutrient pollution from sources like sewage spills or inadequate stormwater systems. Be active in advancing Everglades restoration so that we can reduce the high-volume, nutrient-rich Lake O discharges to the east and west coasts. And stay involved in the fight for clean water as we battle the corrupt and crooked political schemes—like Senate Bill 2508—that benefit special interests at the expense of the people and environment of Florida.
We can turn the tide on Florida’s water crisis, but it’s going to take everyone standing up and speaking up.
We know that a lack of awareness about our water issues is one of the biggest hurdles to overcoming them. People can’t care about these issues if they don’t know that they exist, and our elected officials are never going to make changes if the public doesn’t show that they care. We need as many people involved as possible if we want to really move the needle. So, get involved, get others involved, and use your voice today—join us.
Algal blooms in Florida’s waters have become an increasingly consequential challenge—here’s what you need to know.
Slimy, scummy, ninja-turtle green cyanobacteria. Water staining, breath-stopping red tide blooms. Brown, spider-web growth and muck that smothers beneficial seagrasses.
At varying degrees, when these blooms grow beyond balanced levels, they’re all bad for the health of our waters and water-based economy. Some can have toxic, directly lethal impacts while others slowly lead to environmental destruction by upsetting the natural order in the system, but they all threaten clean water.
And unfortunately, with temperatures heating up and the official start of the rainy season in the rear-view, the potential for widespread blooms is on the rise. So, what exactly are algal blooms? Why are they a threat? What makes some more dangerous than others? And most importantly, what causes them, why have they been getting worse, and how can we mitigate them?
What are algal blooms?
Algae is actually a fundamental part of a waterbody, but that’s only if it’s present in natural, balanced amounts. These plant-like organisms are at the foundation of the marine food chain, and they can help oxygenate the water.
But algae can easily grow out of control, creating what’s called a bloom. When this happens, algae’s role in the ecosystem seemingly shifts from one of beneficial contributor to parasitic threat, adopting “take all, leave nothing” behavior.
If the conditions are right, their growth can go unchecked, and whatever is in their path will likely feel it in one way or another.
What’s the threat?
The most dangerous types of algal blooms are Harmful Algal Blooms (HABs). According to the National Oceanic and Atmospheric Administration (NOAA), HABs occur when colonies of algae “grow out of control and produce toxic or harmful effects on people, fish, shellfish, marine mammals and birds.”
The two major HABs that plague Florida’s waters are Red Tide and Blue-Green Algae, both of which come with a laundry list of problems.
Red Tide
Red tide is caused by a marine dinoflagellate known as Karenia brevis. Blooms form offshore in the Gulf of Mexico, but when conditions are right, they can be moved onshore by upwellings, posing a toxic threat to coastal environments.
“What’s important to note about red tide is that it does produce a neurotoxin that can impact fish, wildlife, and even humans to some degree,” explains James Evans, CEO of Sanibel-Captiva Conservation Foundation, a non-profit that carries out red tide and other water-quality monitoring programs in southwest Florida. When airborne, that neurotoxin—called brevetoxin—can cause respiratory illness and eye irritation in humans.
The effects on marine life are even more severe. Supercharged red tide blooms—like those experienced most recently in 2021, 2018, and 2016—can kill thousands of tons of fish, turtles, dolphins, birds, and marine mammals. Wildlife either succumbs directly to the brevetoxin, or they perish as a result of the low-oxygen, dead zone that’s created by the decaying of other dead fish and red tide cells.
Photo courtesy of Capt. Dustin Pack, Tampa Bay Waterkeeper
Last year, a major red tide event littered the banks of Tampa Bay with dead dolphins and fish, including a couple of half-grand goliath groupers. During the water crisis in 2018, a whale shark washed up on the shores of Sanibel Island, shocking beachgoers.
That dent to our wildlife is bad enough, but it also creates additional health hazards and requires extensive, expensive clean-up for the community, all of which affects local real estate and water-based businesses like hotels, restaurants, fishing guides, and more. “It’s really a harmful algal bloom for a number of reasons,” notes Evans. “It’s harmful to the fish and wildlife, but it’s also harmful to human health, and it’s harmful to our economy.”
Red tide discussion with James Evans, CEO of SCCF
Blue-Green Algae
Often neon green in color, toxic blue-green algae blooms (technically a type of photosynthetic bacteria known as cyanobacteria) can stack up in stagnant water and create out-of-this-world scenes. The consequences of blue-green algae are similar to those of red tide, but they most directly affect fresh and brackish waterbodies—where they form—rather than saltwater or estuarine environments.
The most common species found in Lake Okeechobee and the St. Lucie and Caloosahatchee rivers is Microsystis, which produces microsystin, a potent liver toxin and possible human carcinogen.
These toxins can be absorbed through ingestion, direct contact, or by breathing in contaminated air. Research has shown cyanobacteria particles aerosolize and travel miles from blooms, which in Lake Okeechobee can regularly reach concentrations that surpass the EPA’s “safe for human contact” threshold by over 100 times.
Pets have died from drinking contaminated water, and humans can experience acute symptoms like rashes, stomach cramps, nausea, diarrhea, vomiting, and respiratory irritation. Because the long-term effects of blue-green algae on humans are not widely understood, they have become the focus of recent research efforts, like this ongoing study by the University of Miami.
Economic Impacts of HABs
Needless to say, the threats posed by a severe red tide bloom or blue-green algae outbreak can easily turn affected waterways or beaches into no-go zones. They can effectively shut down entire water-based communities, and in Florida’s tourism-fueled economy, that can be devastating.
In a 2020 report, the University of Florida investigated the economic impacts of the 2018 water crisis. Using survey results and Airbnb reservation statistics, the study estimated that event led to $184 million in direct losses to the tourism industry in Florida. It also found that charter/for-hire businesses averaged a 61% decrease in revenue when red tide was present in their areas.
But that’s just the tip of the iceberg, and it’s only the initial wave of damage that algal blooms can incur. There are longer-term, more subtle impacts working beneath the surface too.
Indirect effects of algal blooms
The widespread overabundance of algae in Florida’s waters (beyond just red tide and blue-green algae) can have cascading effects on our marine ecosystems. It’s not just the direct poisoning, it’s also the loss of critical habitat—like seagrasses—that can put the casualty count over the top.
When certain types of marine algae grow beyond natural levels, it can throw off an ecosystem in a number of ways. We already mentioned the oxygen depletion caused by decomposing red tide, which leads to dead zones in the water and secondary fish kills, but some algae can grow so thick, they kill other life-sustaining aquatic vegetation too.
Essentially, when some blooms grow out of control, they block sunlight from reaching other vegetation—like seagrasses—preventing photosynthesis and killing the plant. That’s been the peril of the Indian River Lagoon over the past decade, where repeated harmful algal blooms have led to the loss of more than half of all the seagrass found in the 150-mile east-coast estuary.
Now, the lagoon is struggling to support the biodiversity that’s earned it federal recognition as an Estuary of National Significance, and the loss of seagrass has taken a hit on the entire food chain. “That loss of seagrass and those water quality problems are impacting our biological resources all the way up the food chain, including manatees and our fisheries,” says Duane De Freese, Executive Director of the IRL Council and the Indian River Lagoon National Estuary Program.
Baitfish, shrimp, and crabs have nowhere to hide; game fish have nowhere to chase bait; and treasured species like manatees have lost their primary forage. The situation is a sure crisis—one that’s spiked manatee deaths to record levels and instigated hail-Mary projects like this one that desperately resorts to feeding Florida’s gentle giants with lettuce.
Similarly on the west coast, we’re seeing mass swaths of drift algae replacing seagrasses at an act-now-or-regret-it-later rate. Giant rafts of brown algae known as Lyngbya clutter up Charlotte Harbor’s eastern shores, looking and smelling like a sewage treatment plant. Former seagrass flats are now barren expanses or covered in green algae.
Turtle Grass and Shoal Grass are getting harder and harder to find. In fact, according to the South Florida Water Management District, Charlotte Harbor lost 23% of its seagrasses between 2018 and 2021—that’s 4,500 acres, which represents 30 years of recovery growth.
The worst part is, seagrasses help stabilize and clean our waters, so when we lose them, the cycle is perpetuated. And unfortunately, the problem isn’t limited to the Indian River Lagoon and Charlotte Harbor, we’re seeing it all over the state.
How did we get here?
So, what’s causing these out-of-control events, and how do we mitigate them?
Like other plants, these algae use sunlight, water, and nutrients to grow. Right now, Florida’s waters are heavily polluted with excess nutrients, like nitrogen and phosphorus, and they’re fueling these blooms to unprecedented levels.
Under normal conditions, nutrient levels in an aquatic ecosystem support a balanced growth of grasses, algae, and other marine life. However, when land-based activities introduce excess nutrients into the system, fast-growing algae, like red tide and blue-green algae, have a competitive advantage.
That’s what has been plaguing Florida for years. Nutrient pollution from a variety of sources like stormwater runoff, sewage spills, faulty septic tanks, old phosphate mines, agriculture, and Lake Okeechobee discharges create an environment prime for algal growth.
And although that cause-and-effect relationship has been assumed for many years, it took until very recently to confirm it with scientific evidence. However, a new study published by the University of Florida has directly linked manmade nutrient pollution, like the nitrogen-laden high-volume Lake Okeechobee discharges, to intensifying red tide blooms.
The study, spearheaded by UF’s Center for Coastal Solutions, concluded that “nitrogen-enriched Caloosahatchee River discharges have consistently intensified K. brevis [Red Tide] blooms to varying degrees over time.” Simply stated, the nutrient-rich discharges make red tide blooms worse.
What do we do about it?
Many municipalities will implement their annual fertilizer bans within the next few days, usually kicking off around June 1st every year and continuing through the wet season. That ban is intended to keep rainfall from washing nutrients in lawn fertilizers into our waters, which is great, but it’s only a small fraction of the problem.
There are many other, larger contributors and polluters that individual citizens have much less—if any—direct control over. Ultimately, it’s up to the state to create and strictly enforce more meaningful policy to prevent all nutrient pollution from entering our waters. Thankfully, that’s where the people can influence the situation by using their voice to create the pressure for change.
Demand that your city or county prioritize strategies, techniques, and upgraded infrastructure to prevent nutrient pollution from sources like sewage spills or inadequate stormwater systems. Be active in advancing Everglades restoration so that we can reduce the high-volume, nutrient-rich Lake O discharges to the east and west coasts. And stay involved in the fight for clean water as we battle the corrupt and crooked political schemes—like Senate Bill 2508—that benefit special interests at the expense of the people and environment of Florida.
We can turn the tide on Florida’s water crisis, but it’s going to take everyone standing up and speaking up.
We know that a lack of awareness about our water issues is one of the biggest hurdles to overcoming them. People can’t care about these issues if they don’t know that they exist, and our elected officials are never going to make changes if the public doesn’t show that they care. We need as many people involved as possible if we want to really move the needle. So, get involved, get others involved, and use your voice today—join us.