For humans, toxins can also have harmful effects, including diarrhea, nausea, vomiting, skin, eye and throat irritation, allergic reactions, and breathing difficulties. The two most serious types of cyanotoxins—microcystin and anatoxin—can cause liver failure, shock, respiratory arrest, and even death. High levels of exposure typically occur when swimming, diving, and water skiing.
“Reported prevalence of cyanobacterial toxicosis is increasing in both dogs and humans, with year-round risk in warm climates,” says Laura Robinson, small animal veterinarian at Antonio Animal Hospital. She notes that no disproportionate risk has been observed among breeds, age, or sex.
Is this a growing threat?
Studies show that warming temperatures, resulting from climate change, have potential to be a major factor in cyanobacteria growth. At Lake Tahoe, temperatures have increased by nearly 2°F since 1968, peaking in 2015 with an average temperature of 53°F. Lakes are especially sensitive to climate change, as even small changes in temperature affect the ecosystem.
“One concern is potential for earlier starts to cyanobacteria blooms. They will pose a hazard for more of the summer,” says Stumpf. Though he notes that some species grow more effectively in colder temperatures.
According to the U.S. Environmental Protection Agency, harmful algal blooms are flourishing as a result of climate change. Warmer temperatures and heavier rainfall have caused lakes to favor cyanobacteria over eukaryotic algae—or algae that are beneficial to the environment— giving cyanobacteria a competitive edge. In a controlled lab study, cyanobacteria like Microcystis aeruginosa were found to double their population in 1 to 2 days under favorable conditions, whereas many eukaryotic algae might take 2 to 4 days to double under similar conditions.