On a sunny June day on Prairie Lake in Minnesota, the Tatge family was tossing tennis balls in the water for their Labrador, Copper, to catch. But after playing for a few minutes, Copper stumbled to the shoreline and collapsed, obviously in great agony.
The one odd thing about the water that day was the cloud of green slime floating on the surface, recalls Brock Tatge, Copper's owner. Copper died a few hours later at the veterinarian's office. The doctor who examined him believed the retriever died after ingesting toxins from blue-green algae in the water.
Blue-green algae, or cyanobacteria, turn lakes a distinctive hue when conditions are right for the growth of algal blooms. In addition to producing a thick mat of green scum and an offensive smell, sometimes blue-green algae also produce microcystins, toxins that can be deadly to dogs, livestock and other animals within hours of contact.
Typically, when a person looks at the soupy green swamp of a lake overcome with blue-green algae, there's little chance he'll wade in for a swim. But dogs are often not as discerning. They rarely have a problem drinking or swimming in the potentially toxic green water or licking the slimy water off their fur.
And when they ingest the microcystins, the toxins can cause a range of symptoms ranging from mild eye irritation, drooling and diarrhea to extremely serious health issues such as liver failure and even death, according to the Pet Poison Helpline. There is no antidote for the toxins produced by blue-green algae and death can happen within minutes of exposure.
A rise in animal illnesses
The Minnesota Pollution Control Agency started tracking dog deaths related to suspected blue-green algae poisoning about a decade ago. After splashing along the shore of Lake of the Woods in August 2015, a 4-year-old springer spaniel named Layla became the 18th dog on the list, according to Minnesota Public Radio News.
Jack Lundbohm, Layla's owner, told MPRN that the water turns green on the lake nearly every summer. But he didn't start seeing the unmistakable crud of cyanobacteria until recently.
"The blue-green algae is a totally different beast," he said. "When it blooms, it's an awful sight. It floats in the water like a big raft. It's almost metallic blue and green in color, and when you drive through with your boat, it has a very strong metallic odor that you just have to wish you'd never smelled before."
A 2019 study by Stanford University and NASA researchers found that potentially toxic algae blooms have become more frequent and intense in freshwater lakes around the world since the 1980s. Using satellite imagery, they studied 71 lakes in 33 countries on six continents, watching how the algae changed over 30 years. They found that in 68% of the lakes, peak summertime algae blooms got worse, while intensity only decreased in 8% of the lakes.
Their findings, published in the journal Nature, suggest that these harmful algae blooms are becoming more common globally. The authors say this "counters the hypothesis that increased reporting of toxic blooms is instead a byproduct of increased scientific attention."
Similarly, a study published in the journal Toxins uncovered 368 cases of dogs that either died or became sick from blue-green algae in the U.S. between the late 1920s and 2012. Cases were reported sporadically, according to the study, until the mid-'70s when cases occurred "almost yearly."
More recently, between 2007 and 2011, 13 states reported 67 confirmed or suspected cases of dog illnesses associated with blue-green algae; more than half of the cases were fatal.
The report detailed how the researchers believed the dogs were exposed to the toxins:
- Inhalation – 13%
- Ingestion – 9%
- Skin contact plus ingestion (swimming, with swallowing water or licking fur) – 54%
- Unknown – 24%
The dogs' symptoms included vomiting and diarrhea, lethargy and neurological signs, including stumbling and behavioral changes.
Where blue-green algae lives
Cyanobacteria isn't limited to the occasional lake or ocean on a hot summer day.
"You'll find it everywhere," says Ohio State University environmental biologist Dr. Jeffrey M. Reutter, past director the Ohio Sea Grant College Program. "It's very naturally occurring. In fact, a good deal of the oxygen we breathe is produced by cyanobacteria in the ocean."
Not all species are capable of producing toxins. Only about a dozen of them cause problems when temperatures are warm — typically above 60 degrees Fahrenheit (15 degrees Celsius) — and the nutrient level is high, says Reutter. And for blue-green algae, the nutrient that matters is phosphorous. Because phosphorous levels tend to be higher in summer, that's when the chances of coming across toxic blooms increase.
How to stay safe
One of the problems with cyanobacteria is that you can't tell the difference between a harmless bloom and a toxic bloom just by looking at it, says Reutter.
"Any time you see a really high concentration of the algae, I would stay away."
That means keeping your dog (and your family) away from the water. If your pet happens to get wet, rinse him off with clean tap water, don't let him lick his fur, and get immediate medical attention if he starts showing any unusual symptoms.
But animals are by no means the only ones that can get sick from cyanobacteria.
When people come into contact with cyanobacteria through swimming or jet skiing, symptoms can include skin and eye irritation, headaches, fever, muscle and joint pain, blisters, diarrhea, vomiting and more, according to the Environmental Protection Agency (EPA). Symptoms can appear within a few minutes or a few days. Really severe cases can lead to seizures, liver failure, respiratory arrest and even death.
"When you look at places from around the world, you realize it's not just an Ohio, or U.S. or Canadian problem. There are places where people have been killed from it. It's something to be taken very seriously," says Reutter. "You can measure toxicity a variety of ways and, in some measure, [the bacteria] are more toxic than cyanide."
Editor's note: This story has been updated with new information since it was published in May 2016.