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Cyanobacteria (Blue-Green Algae)

Recently, the issue of blue-green algae (cyanobacteria) and their potential impacts to the environment, natural resources, and public health has earned much attention in the USA.

Common in most of Florida's aquatic environments, many cyanobacteria species are capable of producing harmful toxins (cyanotoxins). Cyanobacteria can cause unsightly blooms; cause taste and odor problems in public water supplies and can kill domestic animals, pets, and fish and wildlife that drink or are otherwise exposed to untreated contaminated water or toxic biota.

Although a major focus for public health officials is cyanotoxins in drinking water supplies, increased concern for the possible risk for human illness through recreational exposure is on the rise. In 2005, the Florida Department of Health issued health advisories recommending people and their pets refrain from recreational use or contact with blue-green algae blooms in both the St. Johns River (Duval, Clay, and St. Johns counties) and the St. Lucie River (Martin County from the Okeechobee Canal to the St. Lucie Inlet).

In recent years, publicity over blue-green algae in central Florida lakes, the St. Johns, St. Lucie, and Caloosahatchee rivers, has led to the FWC receiving enquiries from the public concerned about human health risks and whether fish are safe to eat from affected areas.

Cyanobacterial blooms are common in Florida lakes, rivers, streams, and ponds. Approximately 20 cyanobacteria species in Florida's waters are capable of producing toxins, including bloom forming species of Microcystis, Cylindrospermopsis, Anabaena, Aphanizomenon, Lyngbya, and Planktothrix.

Different cyanobacteria species can produce more than one type of toxin. As with other harmful algal blooms (HABs), cyanobacteria and their toxins can disrupt and damage sensitive ecosystems, and threaten public and natural resources health and the environment.  The public may be at risk if they ingest untreated drinking water from affected areas, or possibly from recreational exposure to toxins.

Cyanobacteria blooms are most common in the summer when growth conditions are ideal but may occur at any time of year. There is no standard duration for a bloom and no way to determine visually whether or not a bloom is toxic. Persistent blooms affect many of Florida's largest and most important rivers, lakes, and estuaries including the St. Johns, St. Lucie, and Caloosahatchee rivers and lakes Okeechobee, Apopka, Griffin, and Harris.

Health Threats

There are three main types of cyanotoxins in Florida's freshwater systems: hepatotoxins (affecting the liver), neurotoxins (affecting the nervous system), or dermatotoxins (causing topical skin irritations).

To date, very few cases of human illness related cyanobacteria incidents have been reported in the U.S. In Florida's freshwater systems, some toxic cyanobacteria such as Microcystis, commonly form blooms that can, on occasion, appear in lakes and rivers and in reservoir waters destined for drinking water use. These water treatment plants are designed to remove bad odors and taste associated with blue-green algae blooms and to extract toxins from the source water.

Recreational exposure by direct contact with a cyanobacteria bloom from activities such as jet-skiing, boating, and swimming have been reported to cause hay fever-like symptoms (itchy eyes, sore throat, congestion) and dermal reactions (skin rashes, blistering) at high concentrations. Ingesting contaminated water can cause gastrointestinal distress (diarrhea, abdominal pains, nausea, vomiting). Low level chronic exposure of contaminates through water or fish have yet to be studied.

The risks of cyanotoxins to natural resources remain relatively unknown. Health problems may occur in animals if they are chronically exposed to fresh water with cyanotoxins.

Livestock and domestic animals can be poisoned by drinking contaminated water, and fish and bird deaths have been reported in Florida water bodies with persistent cyanobacteria blooms.

It is important to remember these toxins have no known antidotes and cannot be removed by boiling.

Health Tips

The Florida Department of Health (DOH) advocates a common sense approach to eating fish and participating in recreational water activities where blue-green algae blooms occur.

To reduce your risk of exposure:

  • Avoid scummy, foamy water where algae mats are present (Heavy blooms often appear as bright or pea green to reddish-brown water, occasionally with a "paint scum" appearance due to dead algae, and may emit unpleasant gassy odors.)
  • Don't cook with, eat fish from, or drink scummy water
  • Do not let your pets or children eat or drink from affected waters
  • Don't eat fish that look unhealthy
  • Do not harvest dead or dying fish or shellfish
  • Do not swim in, jet ski over, or play near scummy water or algal mats
  • Do not allow your pets or children to swim in, drink from, or play near scummy water
  • Do not irrigate with scummy water
  • Do not use herbicides to kill blooms (this can release the toxins directly into the water)
  • Minimize nutrient runoff and use of fertilizers (this reduces the risk of a potential harmful bloom occurring)
  • If contact with suspect or contaminated water occurs, wash off immediately and thoroughly with clean water and soap (make sure to rinse the swimsuit areas and your pets' fur). Consult a doctor if illness occurs. Contact a veterinarian if your pet suddenly becomes lethargic or shows signs of poisoning including vomiting, diarrhea, or seizures.


Report any change in the taste, smell, or color of your public drinking water to your local utility. You may also contact your local county health department's environmental health program.

In the event someone suspects they may have become sick from exposure to blue-green algae, the DOH recommends they call the toll free Poison Control Center at 800-222-1222. The hotline is staffed by health professionals 24/7 every day of the year.  The DOH works with doctors to help alert for potential problems after contact with cyanobacteria. Early detection helps regulate events allowing county health departments to place health advisories into effect.

Blue-green algae blooms along with dead, diseased, or abnormally behaving fish or wildlife can be reported to the FWC's Fish and Wildlife Research Institute (FWRI) Fish Kill Hotline (online) or by phone at 800-636-0511. A biologist will respond or a recorded message asking callers to leave contact information and a detailed report.

NOTE: The Fish Kill Hotline should not be used to request dead fish cleanup, this is the responsibility of local authorities, not state agencies.