As the articles point out, dogs are often the first alert to freshwater dangers. Their willingness to swim in and drink slimy water makes them sentinels for some of the most powerful natural poisons on earth.
A Labrador Retriever enjoying a family outing in June 2015 collapsed after swimming in a Minnesota lake. He died that day at the vet’s office. While tests were pending, the vet suspected that the dog was poisoned by cyanobacteria, also known as blue-green algae (BGA).
While most algae are harmless, some species of blue-green algae produce toxins that can kill a dog within minutes. Those that survive, or dogs who are often exposed to low levels of toxins, may develop health problems such as chronic liver disease and possibly tumors—damage that may go unnoticed until it’s severe. Humans can be sickened, too, though deaths are rare.
Dog deaths are another matter.
As health agencies weigh the human risks that lie in recreational and drinking water from harmful algal blooms, they’ve been looking closely at animal deaths.
In New Mexico, 100 elk died in August 2013 after drinking water tainted with blue-green algae. When it comes to pets, researchers suspect many deaths are missed because people don’t even realize their dogs were exposed. Vets may not recognize the symptoms, and tests to detect the toxins can be costly and complex.
A study published in 2013 found 368 cases of dogs that died or were sickened by blue-green algae in the U.S. between the late 1920s and 2012. The authors say these “likely represent a small fraction of cases” in the U.S. each year. “The vast majority of blue-green algae associated dog deaths remain unreported and often unrecognized by owners and veterinarians.”
And the cases have surged along with the number of toxic blooms fueled by nutrients such as phosphorous and nitrogen washed into waterways from agriculture, lawns and other sources—and by climate change.
Reports of canine poisonings were sporadic until the mid-1970s, when dog deaths attributed to blue-green algae were reported “almost yearly,” the study notes.
In 2007, as drought plagued much of the country, the Minnesota lake region alone saw as many as 40 cases of canine algae poisoning, and at least four deaths. Since 2001, eleven dog deaths have been blamed on blue-green algae in California’s Humboldt and Mendocino Counties.
The earliest known case in the U.S. was in the late 1920s when a dog swam in California’s Clear Lake during an algal bloom. The dog reportedly became ill after licking “a thick coating of algae” from its fur. In 2013, another dog sickened after playing in the lake was less fortunate... this dog did not survive.
Spotting Blue-Green Algae
There are plenty of clues for telling blue-green algae—the most primitive group of algae—from harmless green, brown, and other kinds. But according to a fact sheet [PDF] from the Humboldt County Health Department, while most blue-green algae blooms don’t produce toxins, only tests can tell. “All blooms should be considered potentially toxic.” Only “a few mouthfuls of algae-contaminated water may result in fatal poisoning.”
For one thing, its color isn’t always blue-green. It can also be reddish-purple or brown, and other hues. And not all blue-green species produce toxins, while the dozens that do are only toxic at certain times. Normally, algae are equally distributed throughout the water. But excess nutrients, heat and drought make for large blooms, followed by large die offs. As it decays, toxins are released. These can still taint the water after it looks clear. Blooms may last for a week; their toxins may last three weeks.
Even when blue-green algae isn’t floating on the surface, it may lurk below, moving up and down with available light and nutrients. At night it often floats to the top, forming scum. So blooms can appear overnight.
Wind and waves can then concentrate toxic blooms in shallow areas or at the water’s edge—right where dogs like to splash, wade or drink. The water doesn’t taste bad, vets say, so dogs will lap it up. Some like to gobble down dried algae mats.
After the sudden death of a dog in July 2014—hours after swimming in an Oregon reservoir—officials issued an alert, as they did in Minnesota. But toxic blooms and dog deaths were nothing new. According to Minnesota Department of Natural Resources, from 2004 through 2007, the state had reports of eight algae-related dog deaths, while toxic blooms are a familiar scourge at the Oregon reservoir.
At least 18 states have monitoring programs to detect harmful blooms. But sometimes, even advisories aren’t enough. After two dogs died within hours of drinking water from a private lake in Nebraska in 2004, state agencies acted quickly. Two weeks later, monitoring and notification networks were in place. But by the end of the recreation season there were reports of three more dog deaths, wildlife and livestock deaths, and more than 50 cases of human effects at Nebraska lakes.
The Environmental Protection Agency published a set of national standards for microcystins and cylindrospermopsin (blue-green algae toxins) in recreational or drinking water in May 2019, and promotes safety and public awareness to help protect dogs and kids.
While most algal blooms just make the water unappealing, an EPA information sheet says, “there are some real risks if dogs swim in, wade, or drink from water” with harmful algal blooms. The toxins “can sicken pets, causing everything from mild eye irritations and diarrhea to extreme health problems, including liver poisoning and even death.”
The EPA recommends that outings with pets to lakes, rivers and streams include an algae check. Dogs should not drink, swim or wade in water that is discolored, smells bad, or where there are mats of algae, foam or scum. If dogs do get into scummy water, rinse it off with tap water immediately, making sure they don’t lick algae from their fur. The toxins can also be absorbed through their skin. If a dog shows signs of poisoning, seek veterinary treatment right away. And report incidents to the Public Health Department. To avoid adding to the algae problem at home, the agency advises not over fertilizing.
According to the study of canine incidents, blue-green algae toxins can be inhaled and ingested, and exposure can induce “acute, sub-acute or chronic poisoning” in animals and people.
Most reported dog deaths involved swimming in or drinking from lakes, rivers and other fresh waters where slime was visible. In California, blue-green algae from freshwater tributaries drained into Monterey Bay, killing sea otters in 2010. Scientists were baffled by the deaths. They hadn’t known the toxins could reach the ocean. One major clue: suspicious dog deaths at a lake tainted with blue-green algae that drains to the sea.
Other dog incidents may have involved beach outings. The study of canine cases says that between 2007 and 2010, at least eight dogs developed serious or fatal liver disease after visiting Monterey-area beaches. Two of the dogs belonged to local veterinarians, but weren’t tested for the toxin that was killing sea otters.
Blue Green Algae Toxins, Symptoms and Treatment
Are water-loving dog breeds more at risk for blue-gree algae poisoning? Researchers warn that diagnosing algae poisoning is hard enough—such assumptions can lead to the wrong diagnosis. But the study did find that the most poisoning incidents involved Labrador Retrievers.
However, the “wide range” of affected dogs included Poodles, Dachshunds and toy breeds, which also encountered blue-green algae in urban and residential water bodies. These waters, often shallow and stagnant in warmer months, can have high levels of nutrients escaped from nearby yards and gardens, “providing ideal conditions for toxic blooms.”
The belief that small dogs or urban-dwelling dogs don’t encounter algae may influence the diagnoses considered. Also adding to the problem of detection and treatment, the study claims: the tests are expensive and can take weeks, access to testing may be limited, and diagnosis may not be a priority for the owner after the dog has died.
According to the algae fact sheet from Humboldt County, the toxins of concern are nervous system poisons (neurotoxins) and liver poisons (hepatotoxins). The neurotoxins can kill animals within minutes by paralyzing respiratory muscles, while hepatotoxins can cause death within hours by causing blood to pool in the liver.
The canine study mentions the many reports of animals drinking algae-tainted water “and dying within hours from neurotoxicity or hepatotoxicity, or developing sublethal chronic liver disease.”
Another less dangerous compound causes allergic responses. But initial, low-level exposure to any of these toxins may cause skin irritation and stomach upset, the study says. So those symptoms alone may not help identify the toxin.
Both nervous system toxins and liver toxins can be fatal. Liver toxins cause weakness, vomiting, pale mucous membranes and diarrhea. Common signs of neurotoxins are muscle tremors, seizures, labored breathing and difficulty moving.
Often implicated in poisonings are anatoxins (neurotoxins) and microcystins (liver toxins, considered more common and possibly carcinogenic, research suggests). Dogs are especially susceptible to anatoxins, according to the North Carolina Department of Health’s website; these poisons can be fatal within minutes–or hours. Quick veterinary care with anti-seizure medication and oxygen may help.
The consensus is that there is no antidote for blue-green algae toxins. But the review of dog poisonings says that most exposed animals aren’t given specific treatment, even though “simple, cost-effective treatments may improve their chances.” In the case of microcystin exposure, since many believe that no therapies exist, owners and vets “might euthanize suspect cases or provide limited supportive care.”
After several days of veterinary treatment, a Miniature Australian Shepherd sickened by algae at a Montana lake was only getting worse. On the fifth day, her vets tried a new therapy not readily available. A 2013 report described what happened next as possibly the “first successful treatment of microcystin poisoning.”
Over the next few days the little Aussie made a surprising comeback.
After eight long days, that dog went home.