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The Florida Department of Health works to protect, promote & improve the health of all people in Florida through integrated state, county & community efforts.

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HABs: Harmful Algae Blooms


image of ocean with algae bloom

Algae are plant-like organisms that sustain marine life. They contribute to the food chain and to the oxygen that keeps water bodies healthy. But sometimes, when conditions are right—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 or HABs. In Florida, we find HABs along our saltwater, freshwater and brackish water bodies.

HABs are temporary and usually happen in late summer or early fall. They can last three to five months, sometimes longer, and can affect small and large areas.

As some HABs decay they release a bad odor. Hydrogen sulfide is one such foul smelling gas that is a naturally occurring, 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.

HABs and Animal Health Resources

There are many HAB species in the Gulf of Mexico—Karenia brevis is Florida’s most common red tide organism. Dark red or brown, sometimes with a yellowish tint, this red tide produces brevetoxins that can kill marine animals, and make land animals and people sick. If you’ve been around red tide, you may have had the “red tide tickle”: the itchy throat and cough caused by breathing in brevetoxins that have been released into the air and water when wind and waves break open the cells of the algae.

SYMPTOMS? Stay away from red tide.  Even if you’re not prone to respiratory issues you should be careful: these toxins can cause breathing problems, and can irritate your eyes, nose and throat. Reactions to red tide are worse for people with asthma, emphysema, bronchitis or any chronic lung disease. If you have health issues, stay away from areas with red tide. Pets can become sick from red tide so keep them away from those areas, and contaminated marine animals and fish.

If you come into contact with red tide, wash off with soap and water. 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 don’t get better, see a doctor.

SWIMMING  Don’t swim in or around red tide because the toxin can cause skin irritation, rashes and burning and sore eyes.

DEAD FISH  Red tides can kill fish and other marine life—avoid contact and don’t swim or walk in these areas. Keep your pets away from these areas.

RED TIDE AND FISH  Don’t 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.

RED TIDE AND SHELLFISH   Check local harvesting status at Florida Department of Agriculture and Consumer Services. Crabs, lobsters, shrimp, clams, oysters 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 free of toxin but the rest of the scallop is not (recipes using scallop muscle are safe to eat). Your safest choice is to not harvest or eat shellfish from 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; and slurred speech and dizziness. Neurological symptoms can progress to partial paralysis and respiratory problems.


 image with text blue green algae

In water bodies with blue-green algae, if people or animals splash or if boats create wakes, the cyanotoxins in the algae can release into the air. The toxins mix with water droplets and spray—that’s how people and animals can inhale the toxin. These toxins can’t pass through your skin easily so swallowing large amounts of contaminated water is what causes illness. This algae is blue, bright green, brown or red, and can have a strong odor like rotting plants. Pets can become sick from blue-green algae so keep them out of those areas and away from contaminated marine animals and fish.

SYMPTOMS? Stay away from blue-green algae.  For some people, blue-green algae can cause rashes, stomach cramps, nausea, diarrhea and vomiting. People who are very sensitive to smells can have respiratory irritation. Sometimes, high exposures of toxin can affect the liver and nervous system.
If you come into contact with blue-green algae, get out of the area and wash off with soap and water. See your doctor if you think blue-green algae has made you sick.

CONTAMINATED WATER  Water from areas with blue-green algae can make animals and people sick—stay away from these areas.

SWIMMING  Don’t swim in or around blue-green algae.

BLUE-GREEN ALGAE AND FISH  Fish tested from water with blue-green algae show that cyanotoxins don’t accumulate much in the edible parts—muscle or fillet—of fish, but can in other organs. Rinse fish fillets with tap or bottled water. Throw out guts. Cook fish well.