Red Tide

HABs: Harmful Algae Blooms

Algae are plant-like organisms that sustain marine life. They contribute to the food chain and to the oxygen that keeps waterbodies healthy, but sometimes, when conditions are right—often warm water and increased nutrients—certain algae can quickly grow and overpopulate.

These foam or scum-like masses are called blooms and can be pushed to the shore by winds, waves, tides, and currents. Some blooms release toxins that make ecosystems, animals, and people sick. Scientists call these harmful algae blooms, known as HABs. In Florida, HABs can be found among our saltwater, freshwater, and brackish waterbodies.

HABs usually happen in summer or early fall and can affect small and large areas of a waterbody. Blooms can move around and change in a waterbody due to tides, winds, and naturally fluctuating amounts of the algae. While a specific location might not constantly have a bloom, the bloom itself can continue for weeks, months, or over a year.

As some HABs decay, they release a bad odor due to hydrogen sulfide, a foul smelling gas that is a naturally occurring and colorless product of decomposition. It can smell like rotten eggs. The human nose is very sensitive and can smell the unpleasant odor of hydrogen sulfide at very low levels.

The Florida Department of Health completed testing in 2016 and 2018 for the presence of hydrogen sulfide in the air during HAB events. The results from both studies indicated very low, non-hazardous levels. The smell can cause respiratory irritation, but is not harmful to your health.

• If you are irritated by the strong odor or have breathing difficulties, move away from the source of the smell.
• Symptoms should end a short time after the odor disappears or the exposure to the odor ends.

Animals can also be impacted by harmful algal blooms. For more information available to veterinarians and pet owners, see Education and Resources.

There are many HAB species in the Gulf of Mexico.  Karenia brevis (K. brevis), a single-celled, naturally occurring organism belonging to a group of algae called dinoflagellates, is the common cause of red tide in Florida.

Red tide can discolor water to appear red or brown, and it produces potent neurotoxins, called brevetoxins, that can be harmful to the health of both people and animals. Brevetoxins can be released into the air or water when wind and waves break open the algae cells. Respiratory irritation can occur when exposed to brevetoxins.

Health Impacts

Even if you are not prone to respiratory issues, you should be careful. Red tide can cause coughing and sneezing, and can irritate your eyes, nose, and throat. Reactions to red tide can be worse for people with asthma, emphysema, bronchitis, or any chronic lung disease.

• You can get relief from respiratory symptoms by being in an air-conditioned space.
• For people without asthma or chronic respiratory problems, over-the-counter antihistamines can help.

If your symptoms do not improve, contact or visit a doctor or call the Florida Poison Information Center at 1-800-222-1222.

Avoid Exposure

Do not swim in or around red tide because the toxin can cause skin irritation, rashes, burning, and sore eyes.  If you come into contact with red tide, wash off with soap and water, especially if your skin is easily irritated. 

Fish Kills

Red tides can kill fish and other marine life. Avoid areas where dead fish can be seen - don’t swim or walk in these areas. Additionally, keep your pets away from these areas.

Consuming Fish

Do not harvest or eat distressed or dead fish (or any animals) from or near a red tide.

Fish caught live and healthy can be eaten if filleted and rinsed thoroughly with fresh water.

Consuming Shellfish

Check local harvesting status at Florida Department of Agriculture and Consumer Services. 

Bivalve mollusks, including clams, oysters, mussels, and scallops are filter feeders that can concentrate toxins. These and other shellfish, if harvested from red tide areas, can be contaminated with brevetoxins. The muscle of the scallop is generally free of toxin but the rest of the scallop is not. Marine gastropods, commonly called sea snails (conch, whelk, etc), feed on the bivalves, and can also be contaminated with brevetoxins during a red tide.

Your safest choice is to not harvest or eat molluscan shellfish or marine gastropods from red tide affected areas. 

You could suffer from neurotoxic shellfish poisoning (NSP) if you eat contaminated shellfish. NSP symptoms include:

• Nausea and vomiting
• Tingling of the mouth, lips, and tongue
• Slurred speech
• Dizziness

Neurological symptoms can progress to partial paralysis and respiratory problems.

The latest Red Tide current status maps and testing results are available from the Fish and Wildlife Conservation Commission Website.

^{(SOURCE: DOH HABs; Last Reviewed Dec 19, 2024)}

What should I do if I see an algal bloom?

RED TIDE BLOOMS Reports related to red tide should be directed to Florida Fish and Wildlife Conservation Commission.

TO REPORT FISH KILLS, contact the Fish and Wildlife Health Group at the Florida Fish and Wildlife Conservation Commission's (FWC) Fish and Wildlife Research Institute by calling 1-800-636-0511 or submitting an online report.

REPORT SYMPTOMS from exposure to a harmful algal bloom or any aquatic toxin to the Florida Poison Information Center by calling 1-800-222-1222 to speak with a poison specialist immediately.

DISEASE REPORTING information can be found on DOH's Disease Reporting Information for Health Care and Laboratory Providers Website.

CONTACT YOUR VETERINARIAN if you believe your pet has become ill after consuming or having contact with blue-green algae or red tide contaminated water.

VETERINARIANS can visit the Education and Resources page for more information.

^{(SOURCE: DOH HABs Report & Contact; Last Reviewed Dec 13, 2024)}