RED TIDE FLORIDA

Red Tide is Bad Tide

In Florida, “red tide” is a common term for a harmful algal bloom (HAB) caused by a higher-than-normal concentration of the naturally occurring microscopic alga Karenia brevis.

These blooms produce potent neurotoxins called brevetoxins, which can have severe impacts on marine life (e.g. manatees) and human health. 

Key Characteristics and Causes

• Karenia brevis (K. brevis): This specific species of algae is found almost exclusively in the Gulf of Mexico. When it multiplies rapidly, it can turn the water a discolored hue, often red, brown, or green, though the water may also remain clear.
• Natural Phenomenon: Red tide events are natural occurrences and have been documented in Florida since the 1840s. They typically begin offshore, 10 to 40 miles out in nutrient-poor waters.
• Contributing Factors: Bloom development is complex, involving interactions of biology (the organism), chemistry (nutrients), and physics (wind and currents). While human activity does not cause the initial bloom, nutrient runoff from land (e.g., from agriculture and stormwater) can fuel and prolong a bloom once it moves into coastal areas.
• Duration: Blooms can last for days, weeks, or months, and their location and intensity can change daily with wind and water currents. 

Red Tide Effects and Health Impacts

• Marine Life: Brevetoxins attack the central nervous system of fish, birds, sea turtles, and marine mammals, often resulting in large-scale fish kills and the death of other marine animals that wash ashore.
• Human Health (Respiratory): When wave action breaks open the K. brevis cells, the toxins become airborne in sea spray. Inhaling these toxins can cause respiratory irritation, including coughing, sneezing, and a sore throat. Symptoms are usually temporary, but people with chronic respiratory conditions like asthma or emphysema should avoid affected areas.
• Human Health (Shellfish Poisoning): Shellfish like clams, oysters, and mussels are filter feeders and can accumulate brevetoxins in their tissues. Consuming contaminated shellfish can lead to Neurotoxic Shellfish Poisoning (NSP), which causes gastrointestinal and neurological symptoms such as nausea, vomiting, dizziness, and tingling sensations. Commercial seafood is generally safe due to rigorous monitoring programs.
• Pets: Pets can also be affected by respiratory irritation or by playing with or eating dead fish or contaminated foam on the beach. Pet owners should wash their pets with fresh water if they come in contact with red tide water. 

Red Tide Monitoring and Safety

The Florida Fish and Wildlife Conservation Commission (FWC) and the National Oceanic and Atmospheric Administration (NOAA) actively monitor red tide and issue forecasts for bloom movement and potential respiratory irritation. If you experience symptoms of exposure, you can contact the Florida Poison Information Center at 1-800-222-1222. 

What nutrients contribute to red tide and where do they come from?

Red tide blooms in Florida are fueled primarily by nitrogen and phosphorus. These nutrients come from a variety of natural and human-contributed sources, with human sources having a significant impact on the duration and intensity of a bloom once it moves near the shore. 

Natural Sources

Red tide blooms naturally begin 10 to 40 miles offshore in the Gulf of Mexico, where initial nutrient sources are natural. These include: 

• Deep ocean upwelling: The process where cold, nutrient-rich water from the deep ocean rises to the surface.
• Trichodesmium fixation: A type of blue-green alga called Trichodesmium can “fix” atmospheric nitrogen into a form usable by the red tide organism, Karenia brevis.
• Marine life waste: Nutrients released from zooplankton and microplankton waste and the decomposition of dead marine life.
• Benthic flux: The exchange of nutrients from bottom sediments to the water column. 

Human-Contributed (Anthropogenic) Sources 

Once a red tide bloom is transported into coastal and estuarine environments by wind and currents, it can be fueled and sustained by land-based nutrient runoff. These sources include: 

• Fertilizer Runoff: Excess nitrogen and phosphorus from fertilizers used on residential lawns, golf courses, and agricultural operations are washed into waterways during rainstorms.
• Wastewater and Sewage: Leaking septic systems, discharges from wastewater treatment facilities, and sewage overflows introduce nutrients into the water.
• Stormwater Runoff: Rainwater flowing over urban and suburban areas collects pollutants, including pet waste and other organic matter, carrying them into storm drains, rivers, and ultimately the Gulf.
• Lake Okeechobee Discharges: Nutrient-enriched water releases from Lake Okeechobee down the Caloosahatchee River have been linked to intensified red tide blooms in Southwest Florida.
• Phosphate Mining: Waste products and spills from phosphate mining operations can be a major source of phosphorus pollution in some areas.
• Air Pollution: Nitrogen compounds from vehicle and industrial emissions can enter waterways through atmospheric deposition. 

While human activities do not cause the initial formation of red tide offshore, the influx of human-derived nutrients into coastal waters can significantly increase a bloom’s intensity, size, and duration.

Key Red Tide Impactful Sources

• Lake Okeechobee Discharges: One of the most significant and well-documented sources of nutrients exacerbating red tide in Southwest Florida is the nitrogen and phosphorus-enriched water discharged from Lake Okeechobee via the Caloosahatchee River. These unnatural, managed flows, particularly high-volume releases during the rainy season, introduce a massive nutrient load directly into the estuary and nearby Gulf waters, fueling existing or nascent blooms and making them last longer.
• Agricultural Runoff: Excess fertilizers and animal manure from large-scale agricultural operations in the Lake Okeechobee watershed and the Caloosahatchee River basin are major contributors to the high nutrient levels in the water that eventually flows to the coast.
• Urban and Stormwater Runoff: As water flows over paved surfaces in developed areas, it collects nitrogen and phosphorus from several urban nonpoint sources, including:
  • Residential lawn fertilizers.
  • Pet and yard waste.
  • Leaking septic systems and wastewater treatment discharges.
• Phosphate Mining: The waste products and potential spills from Florida’s phosphate mining industry can be significant point sources of phosphorus pollution in some areas. 

Summary of Red Tide Impact

While red tides originate naturally offshore, the influx of these human-derived nutrients into the coastal environment acts as “food” for the K. brevis algae, allowing blooms to reach higher concentrations, cover larger areas, and persist for much longer durations than they would in a natural system. Studies show a clear link between increased nitrogen coming from the Caloosahatchee River and the intensity of red tide events on the Southwest Florida coast. 

What’s being done to reduce nutrient runoff in SW Florida?

A multi-faceted approach involving large-scale infrastructure projects, implementation of Best Management Practices (BMPs), and local government regulations is underway to reduce nutrient runoff in Southwest Florida

Large-Scale Water Management Projects

The most significant efforts are part of the broader Comprehensive Everglades Restoration Plan (CERP) and the Northern Everglades and Estuaries Protection Program (NEEPP), which aim to store, treat, and move water differently through the landscape. 

• C-43 West Basin Storage Reservoir: This major reservoir is under construction in the Caloosahatchee watershed and is expected to be largely complete by 2025. It will hold a large volume of water during the rainy season to prevent harmful, nutrient-rich discharges to the estuary, and then release it during the dry season to maintain a more natural flow and salinity balance.
• Everglades Agricultural Area (EAA) Reservoir and Stormwater Treatment Area (STA): This project includes a combination of water storage and a constructed wetland (STA) to naturally remove nutrient pollution before water flows south into the Everglades and Florida Bay. The STA component began operation in early 2024.
• Lake Okeechobee System Operating Manual (LOSOM): New operational schedules for Lake Okeechobee are being implemented by the U.S. Army Corps of Engineers and the South Florida Water Management District to better balance flood prevention with water quality needs, aiming to reduce harmful discharges to the coastal estuaries.
• Stormwater Treatment Areas (STAs): The construction and operation of STAs (large, constructed wetlands) in various watersheds are a key strategy to filter nutrients out of the water before it is discharged into natural water bodies. 

Best Management Practices (BMPs)

State agencies, including the Florida Department of Environmental Protection (FDEP) and the Florida Department of Agriculture and Consumer Services (FDACS), mandate or encourage BMPs for both agricultural and urban areas. 

• Agricultural BMPs: Farmers are required to adopt practices such as nutrient management techniques (applying the right amount of fertilizer at the right time), using cover crops to reduce soil erosion, and constructing filter strips to capture runoff on-site.
• Urban BMPs: Local governments and developers are required to implement practices like retaining and treating stormwater on-site, managing landscape waste, and promoting Florida-Friendly Landscaping™ principles that use native plants and reduce water and fertilizer use. 

Local Regulations and Initiatives

Cities and counties in Southwest Florida are implementing specific policies to control nutrient sources. 

• Fertilizer Ordinances: Many local governments have enacted strict fertilizer ordinances. Common rules include a blackout period during the rainy season (typically May 15 to Oct 31) when fertilizer application is prohibited, requiring phosphorus-free fertilizers, and maintaining a buffer zone from water bodies.
• Wastewater Infrastructure Upgrades: There are ongoing efforts and funding for projects that replace old or failing septic systems with connections to central sewage and upgrade wastewater treatment facilities to better remove nutrients.
• Public Education: Non-profit organizations and local governments run campaigns to educate residents on actions they can take to reduce their personal contribution to nutrient pollution, such as picking up pet waste, keeping grass clippings out of storm drains, and maintaining septic systems. 

Effect of Karenia Brevis on the Florida Environment

Courtesy of WIKIPEDIA – Karenia Brevis

Brevetoxins are a group of neurotoxic compounds released by K. brevis. At high concentration these brevetoxins can be fatal to fish, marine mammals, and birds. Brevetoxins also pose a threat to corals.

Large nearshore fish fatalities are caused by red-tide blooms. Shorebirds can also get infected with brevetoxins by consuming fish. Thus, red-tide blooms can have major level effects impacting the whole ecosystem. Additionally infected fish and shellfish pose a threat to the fishing industry and economy.

K. brevis red tides have also been found to be a significant factor in the mortality of multiple species of sea turtles. Specifically Kemp’s ridleys, loggerheads, green turtles, and hawksbills, particularly along the west Florida coast. Since red tide is a major cause of stranded sea turtles, it contributes to the vulnerability of this endangered species.

K. brevis blooms pose other lethal health risks to marine animals like manatees. Extended occurrences of red tide blooms in the Gulf of Mexico have been associated with substantial instances of mortality in manatee populations. Brevetoxins can lower manatee’s immune systems making them more at risk for other diseases. Additionally, brevetoxin has been correlated with oxidative stress in manatees.

Overall brevetoxins have grave effects on wildlife, and the multitude and compounded effects on entire marine ecosystems are not yet fully understood.