Blue-green algae, also called cyanobacteria, are a type of bacteria that occur frequently in Florida’s freshwater environments. Like plants, they undergo photosynthesis, using sunlight and nutrients for growth.
An algal bloom is the rapid and substantial increase in algae biomass in an aquatic system. The accumulation of cells can discolor the water and may produce floating mats that emit unpleasant odors.
Blue-green algae require sunlight and nutrients for growth. Algal blooms can occur in certain environmental conditions. These include warm water temperatures, sunny days, and calm water conditions that allow light to penetrate through the water column. Nutrients that fuel blooms can come from within the aquatic system and/or from land-based nutrients that are moved into the body of water. Many blooms occur following storm events that can stir up nutrients that are trapped in the lake sediments and/or deliver stormwater nutrients from the surrounding watershed.
It is impossible to predict how long a bloom will persist. Blooms can last a few days to a few months or longer. If optimal growth conditions and nutrients persist, so too can a bloom.

Many types of blue-green algae can produce toxins, and algal blooms can result in high toxin concentrations. Toxic blooms can kill fish and other wildlife. Low dissolved oxygen levels in the waterbody can also take place, especially as the bloom starts to decay. These low oxygen events can also result in fish kill events.

Toxin-forming blue-green algae can also result in serious human health effects. Algal toxins are diverse. Depending on the toxin, they can result in gastrointestinal problems and, in extreme cases, liver damage (hepatoxins). They can affect the nervous system and cause respiratory distress (neurotoxins), or they can cause skin and eye irritation. Animals such as pets can also be negatively impacted by these toxins.

The Florida Department of Environmental Protection (DEP) regularly collects water samples to determine the type of blue-green algae present. If the algae identified are known to produce toxins, additional testing is carried out to determine if toxins are present and the toxin concentration. Water samples collected on April 21 at Lake Wauburg confirmed that the dominant blue-green algae in the lake were Microcystis species and microcystin toxin concentration was 8.4 micrograms/L (µ/L). More recent samples were collected on May 4. The dominant species were unchanged and the toxin concentration results was approximately 1.5 µ/L. Water quality results are available at FloridaDEP.gov/AlgalBloom.

Unfortunately, it is impossible to visually tell if a bloom is producing toxins. For this reason, DEP recommends that individuals and pets stay out of water where algae is visibly present or where water is discolored.

People and animals can be exposed to blue-green algal toxins through the ingestion of water, direct contact to the skin or eyes, or inhalation of airborne particles. These exposure routes are most common during recreational water-based activities such as swimming, boating, and sailing. People and pets should not drink, swim, or recreate in water where blue-green algae blooms are present. Windy conditions and water spray may exacerbate inhalation of airborne particles. If individuals experience respiratory irritation they should leave the area. Children, the elderly, and those who are immunocompromised may be at risk even at low concentrations and should avoid exposure. Pets should also avoid drinking or swimming in water where blue-green algae is present. Dogs who come into contact with algae should be rinsed off with fresh water to prevent them from licking their fur. Pets should also be discouraged from chewing on any dead fish or other decayed material.

Source: University of Florida's Institute of Food and Agricultural Sciences (UF/IFAS)
Updated: 5/6/2022

Contact information:
Lisa Krimsky
Water Resources Regional Specialized Agent
University of Florida IFAS