Red Tide

Red Tide

red tide in florida


Red tides, also known as harmful algal blooms or HABs, occur when microscopic algae (phytoplankton) multiply to higher-than-normal concentrations, often discoloring the water. The Florida red tide, Karenia brevis, can be found in bays and estuaries but not in freshwater systems such as lakes and rivers. K. brevis produces brevetoxins capable of killing fish, birds, and other marine animals.  Brevetoxins may also cause health problems in humans that can range from respiratory irritation to Neurotoxic Shellfish Poisoning.  The presence of HABs can also be good indicators of environmental change in the water and on land. 

What are Brevetoxins?

Brevetoxins are neurotoxins (toxins that impair the nervous system) that can affect the body through inhalation (breathing it in), dermal (skin contact), or oral (ingestion) exposure. Illness resulting from exposure can range from respiratory irritation to Neurotoxic Shellfish Poisoning. Wave action can break open K. brevis cells and release these toxins into the air. Mote Marine Laboratory studies have shown that airborne red tide toxins can travel up to a mile inland, depending on the wind direction and other weather patterns. That means, even if you are a few blocks away from the beach, the toxins could still be affecting you.

Good Things to Know

  • When driving, keep your car windows up and the A/C or heat on.
  • For people without asthma or any other chronic respiratory problems, over-the-counter antihistamines may relieve symptoms.  
  • People with chronic respiratory ailments should be especially vigilant about taking prescribed medications daily.
  • If you do feel discomfort, you should also limit your outdoor activities  
  • Always seek medical care if your symptoms worsen.

Red Tide History

Red tide, specifically Florida red tide or Karenia brevis, has been documented in the southern Gulf of Mexico as far back as the 1700s and along Florida's Gulf coast in the 1840s.  In the early 1500s Spanish explorers complained of respiratory distress and illness, and Native Americans told stories of large fish kills.  It occurs in the Gulf of Mexico almost every year, generally in late summer or early fall.  K. brevis, is found almost exclusively in the Gulf of Mexico from Mexico to Florida.  Florida red tides can be transported around the Gulf of Mexico as coastal waters move with winds and currents. Some have even been carried by the Gulf Stream current into the Atlantic Ocean as far north as Delaware.  K. brevis is most common off the central and southwestern coasts of Florida between Clearwater and Sanibel Island.  Most blooms last three to five months and affect hundreds of square miles, but they can continue sporadically for as long as 18 months, affecting thousands of square miles.  

What is the Aquarium is doing?

The Florida Aquarium is ready and available to help.  We have informed all governing agencies that we are available to help in any capacity that is needed.  The clean-up and mitigation of red tide is strongly governed and requires extensive precautions.  


Information presented here was provided by: NOAA – National Oceanic and Atmospheric Association, MOTE Marine Laboratory and Aquarium and FWC - Florida Fish and Wildlife Conservation Commission