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Blue-Green Algae – Not to be Taken Lightly When Recreating in Water

Updated: Dec 14, 2023

August 8, 2023—Summer is upon us and so are temperatures in the 90s and above. States like Arizona, Texas, and Florida are experiencing record-breaking heatwaves. We’re not immune from hot temperatures and heatwaves here in the Pacific Northwest. When the mercury in the thermometer rises, it’s natural for people to head to lakes and rivers to cool off to escape the heat. However, when the temperatures rise, a potential killer often appears in warming bodies of water. That killer: cyanobacteria, commonly called blue-green algae.


At normal levels, cyanobacteria is harmless. In fact, it’s usually present in many lakes and ponds where outdoor recreation activities like swimming and paddling occur with no ill effects to those using the water. It’s when a lake experiences a bloom commonly called an algal bloom, though cyanobacteria isn’t algae but bacteria, that cyanobacteria can become harmful, even deadly (Rastogi et al., 2015). Cyanobacteria blooms occur when oxygen in lakes, ponds, and other waterbodies is depleted due to a rise in water temperature.


Cyanobacteria release toxins called cyanotoxins into the water. The toxins can remain at harmful levels in a lake or pond for weeks. These potent toxins can attack the nervous and endocrine systems, blood stream, and liver. In high enough concentrations, cyanotoxins can be deadly to humans and dogs when the water is consumed. In the summer of 2019, four dogs died from swimming in lakes and ponds contaminated with blue-green algae (Young and McMahon, 2019). It has been reported that deaths in animals can occur within minutes to a few hours after swallowing water containing cyanotoxins (EPA, n.d., Rastogi et al., 2015; Stewart et al., 2006). When cyanotoxins occur in shellfish, they can lead to a shutdown in shellfish harvesting.


Climate change is only expected to increase the frequencies and intensities of the algal blooms (Rastogi et al., 2015). Waterbodies are getting hotter earlier and staying hotter longer. Recently, the water temperature off Marathon Key in Florida was recorded at 101.1° F.


Mitigation against cyanotoxin poisoning entails restricting access to the affected body of water. Symptoms of cyanotoxin poisoning in humans include hay fever-like symptoms, gastrointestinal pain, respiratory distress, vomiting, diarrhea, and skin rashes (EPA, n.d.). Should you come in contact with contaminated water, rinse off with clean, fresh water as soon as possible. Seek medical attention immediately if you think that you have ingested water contaminated with cyanotoxins.


Treatment for dogs is similar to that for humans. Immediately get your dog to a veterinarian if you suspect the dog has ingested cyanotoxins from directly swallowing contaminated water or licking his fur after being in contaminated water. Further information on protecting your dog can be found at www.epa.gov/nutrientpollution/protect-your-pooch. YouTube has a helpful video on protecting your dog from harmful algal blooms.


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