Several reports of scary dog deaths have recently come from the Southeast. The common thread? A toxic bloom of algae in ponds. Here's how to spot it, and keep your pets safe.

By Dan Nosowitz
August 15, 2019

Letting your family pets cool off in water seems like a harmless and fun warm-weather activity, but a few recent water-related incidents suggest otherwise. Reports of dogs dying after swimming in contaminated water have come in from the Southeast—three in North Carolina, one in Georgia, and one in Austin, Texas. The deaths have been connected to a bloom of blue-green algae, which can be found in ponds where dogs like to splash. What is this stuff, and how can you avoid it?

Blue-green algae is technically known as cyanobacteria, a very old organism that can be found across the United States in both freshwater and saltwater. You’re probably familiar with other varieties of algae, especially green algae, which is that slimy, scummy stuff you’ll see in pools, ponds, and even fish tanks. Green algae can look gross, but it isn’t toxic. Blue-green algae, on the other hand, is.

Image courtesy of Getty.

Blue-green algae, confusingly, isn’t technically algae at all—it’s a bacteria—though it looks very similar. It’s most likely to appear in shallow water during hot months like summer and early fall, where the temperature stays above around 75 degrees. With those ideal circumstances, blue-green algae can thrive, but the addition of other chemicals can cause what’s known as an algal bloom. An algal bloom can be caused when runoff of pesticides, fertilizers, and other chemical treatments enter a pond. Blue-green algae loves that stuff, and it can cause it to bloom in huge quantities.

Blue-green algae is toxic; it smells awful, for one thing, and is known to kill fish and other marine life when it blooms. It hasn’t been confirmed yet, but it’s generally believed that this bacteria caused fatal liver failure in these dogs. Dogs can consume the algae after swimming in a pond infested with it, either by drinking the water or licking themselves after swimming

According to the EPA, symptoms can be immediate or delayed, and include vomiting, diarrhea, weakness, and seizures. If you see any of these symptoms, get to the vet immediately. It affects people the same way.

So how can you detect blue-green algal blooms, and keep your dog safe? Unfortunately, it’s incredibly difficult to spot. Despite its name, blue-green algae doesn’t have a consistent blue-green color; it can be blue-green, or green, blue, brown, or red. It might be floating on the surface of a body of water, looking like clumps of plant matter or even just some discoloration in the water. But it also has been known to live, in shallow water, under the surface, attached to rocks and roots. 

If this sounds like there’s basically no way to tell if a body of water has toxic algae in it, well, you’re not wrong. You can look for some warning signs, like “dead zones,” which are areas with no life: no flowers, dead fish, dead frogs, that kind of thing. But that’s not a totally effective way of deciding whether a pond is safe for swimming. The UK government says that if you’re not sure, it's best to assume a body of water is infected, and stay away.

Put simply, you should try to avoid small, stagnant areas of water like ponds during the summer months when algae blooms. Rivers tend to be a better swimming option, as the moving water is less ideal for the algae to thrive. So do your best to keep your dog away from ponds this summer. They may not like it, but it’s for their own good.



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