Blue-Green Algae

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In recent weeks, toxic algae have made the front page of multiple news sources, who have warned of the algae’s toxins. The culprit behind these stories is blue-green algae, which, as it turns out, is not an algae at all, but a bacteria. Blue-green algae are a type of cyanobacteria that are photosynthetic, producing energy from light-like algae while giving them a green color. For this reason, cyanobacteria are usually thought of as beneficial; however, blue-green algae produce cyanotoxins which make humans and animals sick.

Cyanotoxin Exposure

There are multiple ways that cyanotoxins can be absorbed. If you swallow, touch, or breathe in water droplets from water that has blue-green algae you may ingest toxins. Symptoms include vomiting, diarrhea, rash, eye irritation, cough, sore throat, and headache and begin within two days of exposure. Pets are susceptible because they swallow more water while swimming and are more likely to drink the water. Animals can experience symptoms within minutes of exposure to the toxins. Symptoms they might experience include vomiting, diarrhea, weakness, difficulty breathing, and seizures. In the worst cases, animals have died. If your pet experiences these symptoms after exposure to algae, contact a veterinarian.

Blue-Green Algae Identification

Blue-green algae have a characteristic bright green or blue color. They often appear as if someone spilled paint across the surface of the water. This appearance is due to the bacteria’s buoyancy. Most blue-green algae are free-floating and rise to the surface. A simple test known as the “Jar Test” takes advantage of this property. For the Jar Test, a small amount of water is collected in a clear jar and is allowed to settle overnight. If the algae settles to the bottom (left image), it is likely (<98%) that it is not blue-green algae. If it does float and suspend (right image), then it may be blue-green algae. It is important to note that if the test indicates it may be blue-green algae, that does not mean that it is toxic, but rather that it could be toxic. More information on the Jar Test can be found here: Jar Test.

algae in jars

Photo from the Minnesota Pollution Control Agency

Additional Information

The Albemarle Resource Conservation and ​​Development Council is a great resource to track when and where blue-green algae has been detected. Their webpage has an interactive map showing blue-green algae blooms, as well as additional links to educational articles on blue-green algae. The National Centers for Coastal Ocean Science (NCCOS) has more information on algal blooms as well and has a map estimating cyanobacteria biomass, indicating the severity of the threat. Their webpage is linked to the map. For additional help or questions related to blue-green algae, please contact Adam Formella at the N.C. Cooperative Extension of Currituck County office at (252) 232-2262 or by email at