Here in Florida, we are no strangers to algae. It occurs naturally in both saltwater and freshwater ecosystems. Our warm climate, ample sunlight, and slow-moving, shallow waters provide excellent habitats for many algal species. If you have spent time around a pond or lake, you have likely seen common algae, often visible as hairy floating mats, murky water, or plant-like muskgrass. However, you may have also noticed water that looks bright green, aqua, streaked, or simply unnatural. These unusual appearances are often the result of a cyanobacteria, or blue-green algae, bloom.

The Science Behind Cyanobacteria

Commonly known as blue-green algae, cyanobacteria are single-celled microorganisms (bacteria) that naturally exist in fresh, brackish and salt waters, soils, humid rocks, walls, on snow/ice, etc. Despite their everyday name, cyanobacteria lack the specific cell structures required to be classified as ‘true’ algae (eukaryotes). They are grouped as algae because, like plants and other algae, they harness energy from sunlight and release oxygen via photosynthesis.

Blue-Green Algal Blooms

Algae are a natural and essential part of aquatic ecosystems and are always present in small background amounts. They can become problematic when these background concentrations increase into excessive growths, called algal blooms. Blooms are closely tied to high nutrient availability, warm temperatures, and slow-moving water. Human activities often introduce extra nutrients into waterways, pushing concentrations above natural levels. These nutrients act as food for cyanobacteria, and the amount of available nutrients dictates how much the algae can grow. You can learn more about nutrient pollution in urban environments by reading UF/IFAS Publication #SL468.

Identifying an Active Bloom

As the name suggests, cyanobacterial blooms often appear blue-green, but they can also look brown, yellow or reddish. A tell-tale sign of an active bloom is water with a streaked, rippled, or oil-slicked surface. Opaque, green, slow-moving water is another warning sign. Additionally, some cyanobacteria produce a distinct odor resembling potting soil. Severe blooms can even smell like sewage when the algal cells die and decompose.

Health and Safety Considerations

Many species of cyanobacteria produce a range of harmful toxins called cyanotoxins. These include neurotoxins (which affect the central nervous system), hepatotoxins (which affect the liver), and dermatotoxins (which affect the skin). Cyanobacteria and their toxins have also led to respiratory irritations. Not all cyanobacteria produce toxins, and even those species capable of producing toxins do not produce them constantly. Because there is no way to visually tell if a bloom is actively producing toxins, it is best to avoid contact with the water when blooms are present. For guidance, contact your local UF/IFAS Extension Office or use the Extension Foundation’s state-by-state directory if you live outside of Florida.

Reporting Cyanobacterial Blooms

If you spot a suspected cyanobacterial bloom in Florida, it is important to notify the Florida Department of Environmental Protection (FDEP). You can report a new blue-green algae bloom by calling 855-305-3903 or by filling out a short online report on the FDEP website.

NOTE: H. Dail Laughinghouse IV, phycologist/researcher with the UF/IFAS Fort Lauderdale Research and Education Center, contributed to this blog post.

Declaration of Generative AI and AI-assisted technologies in the writing process

During the preparation of this work, the author used AI to optimize accessibility and improve organizational flow. After using this tool/service, the author reviewed and edited the content, and takes full responsibility for the content of the publication

Read More

Florida Department of Health – Harmful Algal Blooms

Florida Department of Environmental Protection – Blue-Green Algae

Florida Fish and Wildlife Conservation Commission – Cyanobacteria

The Science of Harmful Algal Blooms

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