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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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Cyanobacteria/Blue-Green Algae Blooms and Public Health

Aquatic Toxins Program


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How to Keep Your family safe while Enjoying Florida’s Water Ways

Cyanobacteria/ blue-green algae are a group of organisms that can live in freshwater, salt water or
mixed "brackish" water. Most of us know them as "pond scum." These kinds of organisms are naturally occurring in Florida's environment and are also found all over the world. They are part of a healthy ecosystem and help support a wide variety of aquatic life.

When conditions are right, such as warm water and increased nutrients, these organisms can increase in  numbers and accumulate in some areas of a water body. These blooms can sometimes be pushed near  the shore by winds, waves, tides and currents. When this happens, people have a greater chance of contacting the blooms.

Algae blooms are easy to see as many types float on top of the water and are colorful including green, brown, and red. When blooms are present, the Florida Department of Health recommends that people avoid these areas.

You can find additional information on health issues related to algae on the DOH web site for Aquatic Toxins.

To report a human illness related to an algae bloom, please call the

  • Florida Poison Control Center) at 1- 800-222-1222

Toll-free hotlines are available for people to report fish kills and algae blooms:

  • Fish Kill Hotline (Florida Fish and Wildlife Conservation Commission) 800-636-0511
  • Florida Department of Environmental Protection 855-305-3903
More information on cyanobacteria/ blue-green algae blooms can be found in the tabs below:
  • Background
  • Health Studies
  • WHAT ABOUT FISH?
  • How to Avoid Blooms while Enjoying our Waterways
  • How to Keep your Pets Safe
  • Cyanobacteria (Blue-Green Algae) - FAQs
  • Some blue-green algae produce chemicals called cyanotoxins.
  • At high concentrations, cyanotoxins can affect the liver, nervous system and skin.
  • Most problems occur when substantial amounts of water containing high toxin amounts is swallowed such as when people drink untreated surface water.
  • Besides drinking the affected surface water, it is difficult to get cyanotoxins into the body as they do not become easily airborne and do not pass through the skin readily.
  • Most people avoid a blue-green algae bloom because they tend to be icky-looking and smelly.
  • Ecological studies that examine links between environmental conditions and health are meant to be used as a screening tool to generate new ideas as to the cause of health problems that need further research (i.e. hypothesis testing).
  • The results cannot be used as proof of cause for the following reasons:
    • The studies are not designed to link a particular individual’s exposure with the individual's health outcome, meaning there is no way to know whether the disease occurred more frequently in those persons exposed to cyanobacterial toxins that those that were not.
    • Study results may indicate an association between toxin exposure and disease that is not real.
    • Results of ecological studies are even more difficult to interpret when the association between the exposure and disease outcome is complex.
    • Ecological studies also do not account for other risk factors and alternative reasons for a particular disease or symptoms such as underlying inherited health conditions, lifestyle factors, or diet.
    • The toxicity of a substance generally increases as the dose increases. Also, the greater the amount of a substance a person is exposed to, the more likely that health effects will occur. The overall dose a person is exposed to depends on a variety of factors including the concentration of the substance, how often the exposure occurred, how long each exposure lasted and the route of exposure (eating, drinking, or breathing). Ecological studies do not take the exposure dose into account. For example, they don't control for migration of people or length of residency in the area of interest.
    • The studies may also be skewed by differences in the location of a particular exposure versus the location where illness was reported.
Fish tested from water with blue-green algae blooms show that the cyanotoxins from algae do not accumulate much in the edible portion of fish which is the muscle or fillet meat. Exposure to cyanotoxins from catching and eating the fish from areas with blue-green algae is minimal.

Many lakes and rivers in Florida are large with blooms not covering the entire water body. Most of the fish are not in the area where blooms exist. Blooms also tend to be temporary, especially by place and time as they move around due to wind, waves and currents. We suggest that people do not harvest fish near or in the blooms.
  • Do not swim in cyanobacteria/blue-green algae blooms
  • If you come in to contact with the bloom, wash with soap and water
    • Some people who are very sensitive to the algae, may develop a rash.
    • Some people who are very sensitive to smells, may experience respiratory irritation.
  • The Department of Health suggests that people do not harvest fish near or in blooms.
  • Untreated water from the bloom area should not be used for irrigation when people could come into contact with the spray.
  • As always, if you experience an illness, please see your health care provider.
  • Do not allow your pets to swim in the bloom, drink surface water of the bloom or near the bloom, or eat the scum of the bloom.
  • If your pet goes in the water near or in a bloom, do not let them lick their fur and rinse them off.
Frequently Asked Questions: Cyanobacteria/Blue-Green Algae

What are cyanobacteria/blue-green algae?
Blue-green algae are a group of organisms that can live in freshwater, salt-water or in mixed "brackish" water.  Most of us know them as "pond scum." They also have been found to share some characteristics with bacteria, which has led to them being referred to as "cyanobacteria."

What is a cyanobacterial bloom and how do they form?
Cyanobacterial blooms occur when the algae that are normally present grow in numbers more than normal.  Within a few days, a bloom can cause clear water to become cloudy. Winds tend to push some floating blooms to the shore where they become more noticeable. Cyanobacterial blooms can form in warm, slow moving waters that are rich in nutrients. Blooms can occur at any time, but most often occur in late summer or early fall. They can occur in marine, estuarine and fresh waters, but cyanobacteria blooms that can cause concern are those that occur in fresh water, such as drinking water reservoirs or recreational waters.

What do cyanobacterial blooms look like?
Some cyanobacterial blooms can look like foam, scum, or mats on the surface of fresh water lakes and ponds.  The blooms can be blue, bright green, brown, or red and may look like paint floating on the water. Some blooms may not affect the appearance of the water. As algae in a cyanobacterial bloom die, the water may smell bad.

What are some tips for avoiding cyanobacteria/blue-green algae?
It is important that adults, children and pets avoid swimming in or drinking water containing blue-green algae. It is best not to come in to contact with water in areas where you see foam, scum, or mats of algae on the water.  What should I do if I come in contact with cyanobacteria/blue-green algae?  In high amounts, cyanobacteria toxins can affect the liver, nervous system and skin. Abdominal cramps, nausea, diarrhea, and vomiting may occur if untreated water is swallowed. Some people who are sensitive to the algae may develop a rash or respiratory irritation. If you come into contact with an algae bloom, wash with soap and water right away. If you experience an illness, please contact your healthcare provider.

What agency should I contact to report fish kills, algal blooms or illness associated with blue-green algae?
Fish Kill Hotline (Florida Fish & Wildlife Conservation Commission) 1-800-636-0511
Bloom Reporting (Florida Department of Environmental Protection) 1-855-305-3903
Human Illness (Florida Poison Control Center) 1-800-222-1222

Can I eat fish harvested from areas near or in algae blooms?
Fish tested from water with blue-green algae blooms show that the cyanotoxins from algae do not accumulate much in the edible portion of fish which is the muscle or fillet meat. Exposure to cyanotoxins from catching and eating the fish from areas with blue-green algae is minimal.

Many lakes and rivers in Florida are large with blooms not covering the entire water body. Most of the fish are not in the area where blooms exist. Blooms also tend to be temporary, especially by place and time as they move around due to wind, waves and currents. We suggest that people do not harvest fish near or in the blooms.

Is it ok to use algae water for showering or irrigation?
Untreated water from the bloom area should not be used for irrigation when people could come into contact with the spray. Do not use untreated water from an area with a bloom for showering or bathing. 

Where is there more information on algal blooms and health?
Additional information on health issues related to algal blooms is available on the DOH website and the Centers for Disease Control and Prevention webpage. (opens in new window)

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