If your pup likes to swim and splash in ponds, pay attention if one of your favorite watering holes suddenly looks green or smells funny. This time of year, microscopic creatures called cyanobacteria can “bloom,” sometimes creating chemicals that are toxic to animals and people.
This is more of a risk for dogs than for humans because not many people would see a scummy, smelly lake and decide to jump right in (or, for that matter, eat a dead fish they find there). The toxins are most dangerous when swallowed, so if your pup swallows the pond water or licks their fur after they get out, they could be ingesting the toxins.
Where do cyanobacteria blooms occur?
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According to the Centers for Disease Control and Prevention, blooms have occurred in all 50 states and Puerto Rico. They form in warm, slow-moving water, so think ponds and swamps rather than rushing rivers. The blooms occur when the microscopic creatures get a flood of nutrients from the surrounding area, so runoff from sources like farms and septic-tank overflow tends to play a role.
There are other types of blooms, by the way, including those caused by dinoflagellates and diatoms, and these can be toxic, as well. Cyanobacterial blooms occur most often in fresh water, but there can also be toxic blooms in salt and brackish water.
(Nerd fact: Cyanobacteria used to be called “blue-green algae” because they photosynthesize and they are microscopic, like algae. But algae are technically plants, and cyanobacteria are not.)
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How do you know if water is toxic?
It’s not as simple as checking the color, although the appearance of the water can be a big tip-off (especially if the water is normally clear, but has recently changed). The CDC says to look for foam, scum, or mats of algae, and that some blooms look like spilled paint. They can also be other colors, including blue, red, and brown. And sometimes the water will smell like gasoline or rotten eggs.
Sometimes toxic blooms aren’t obvious, though, especially if the algae have formed mats under the surface. Pay attention to warnings that might come from a local health department or that might be posted near lakes. California posts known algal bloom locations on a map on their harmful algal bloom portal.
What happens if my dog swims in the water?
First, get them out, away from the lake, and showered off. This goes for humans, too. It’s possible to be harmed by skin contact with the toxins or even by breathing in tiny droplets of water. Pets may also lick their fur or put their mouth on objects (like a leash) that got soaked in the water, so rinse everything off as soon as you can.
If you’re concerned your pet might have swallowed toxic water, but they haven’t shown symptoms yet, consider calling your vet or the ASPCA Pet Poison Control Hotline at (888) 426-4435. (This is a paid service; your vet might be able to answer questions for free.) Help for humans is available through the regular Poison Control Hotline at 1-800-222-1222 or their website. If you or your pet already have symptoms, skip the hotline and just seek medical care.
Vomiting and diarrhea are possible for you and your pet, and especially keep an eye out for neurological symptoms like dizziness, weakness, or stumbling. Pets may also show excess salivation and convulsions. (If you were in the water, too, you might notice headaches or stomach pain, and you should seek care for yourself.)
If you notice any of these signs, get veterinary care immediately and make sure to mention your pet’s recent swim. Here is the CDC’s guide for veterinarians, which notes that there are no tests or general purpose treatments for cyanobacterial poisoning. Activated charcoal may help if administered right away, though, and in cases where the vet can find out which specific toxin was involved, there are medications that may help.