Friends of the Cornell Riney Canine Health Center,
As we wrap up the summer season, many of us may be thinking about one last weekend of lake trips or warm weather outings with our dogs. Even though Labor Day signals the symbolic end of summer, I am still thinking quite a bit about harmful algal blooms (HABs) as they can occur in the late summer and even early fall. It feels like this year, more than ever, we have been hearing about them popping up across the country. My Pomeranian, Mishka, and I just returned from our beach trip. She loves getting in the water, which tends to surprise most people because of her seemingly coiffed fur, though she mostly ventures in just up to her belly to cool off and wander around. She has not earned champion swimmer status like some of her Labrador friends. I know that keeping an atypical water dog like Mishka out of the water can be a challenge, it is even more important to be aware of HABs for the true water dog breeds that simply cannot get enough swimming.
What exactly are HABs? Freshwater HABs, also known as blue-green algae, are not algae at all. They are formed by a type of microscopic organism called cyanobacteria. These organisms are naturally present in water, but form blooms when they multiply rapidly, often creating mats, streaks, or pea-soup-like discoloration on the surface. HABs are most common during the dog days of summer, roughly early July through mid-August, when water is warm, calm, and nutrient rich. They can start earlier in the spring, depending on the weather, and because water bodies can stay warm into early fall, blooms may persist into September, meaning HABs are still very much a concern for you and your canine companions.
So, are HABs becoming more common, or are we just hearing more about them? While cyanobacteria are nothing new, and are a natural part of water systems, we are seeing overgrowth more often now because of warming temperatures and increased nutrient runoff from things like fertilizers, pet waste, septic systems, and stormwater. These nutrients act like a “superfood” for the bacteria, allowing them to grow rapidly.
While not all blooms are toxic, it is impossible to tell just by looking at the water. The most serious type of toxic blooms can affect either the liver or the nervous system. Symptoms of exposure can appear quickly, within minutes to hours, and depending on the type of toxin, may include vomiting, drooling, or diarrhea, weakness, tremors, or seizures, difficulty breathing or disorientation, collapse, or even sudden death. Dogs are particularly vulnerable because they tend to have fewer discriminating behaviors, meaning they are not too bothered by unsightly or stinky things and are more likely to swim or even drink water from a potentially contaminated source. They can also ingest toxins while grooming themselves after a swim. What makes HAB exposure especially concerning is that there is no antidote, only supportive veterinary care. If you suspect exposure, it is critical to immediately rinse your dog thoroughly with fresh water, prevent them from licking their fur, and immediately contact an emergency veterinarian and pet poison control center.
Since there is no antidote and the effects can be so serious, prevention is paramount. The most advice is, “when in doubt, stay out.” If the water looks suspicious, discolored, foamy, streaky, or smells bad, keep your dog out. Always follow public warning signs and check local advisories before trips to lakes. Many states, counties, or municipalities post warnings when HABs are present. In New York, the DEC provides HAB reporting resources, and wherever you live, your local public health or environmental agencies are the best source for alerts. Rinsing your dog after swimming, even if the water seems safe, is always good practice.
Private water sources, like backyard ponds, carry the same risks. You can reduce HABs on your property by limiting fertilizer use near the water, planting native vegetation along the shoreline to filter runoff, preventing leaves, clippings, and pet or livestock waste from entering the water source, maintaining septic systems, and using aeration or a fountain to keep water moving.
After a bloom, how do you know when it is safe to swim again? For public water in NY, the DEC requires that a bloom be no longer visible for at least 24 hours and that water tests show toxin levels below a certain threshold before reopening swimming areas. Check your local advisories for each state to see how they handle reopening. If you manage water on your private property, it’s safest to wait several days after a bloom disappears since some toxins can remain in the water even after the bloom visually disappears, or even have the water tested, if possible, before letting your dog swim. At a minimum, wait at least 24 hours after all visual signs of a bloom disappear.
While I focused mostly on freshwater HABs, there are saltwater HABs too, sometimes called “red tides.” These are produced by different organisms (algae, instead of bacteria), such as dinoflagellates. Marine toxins can also affect the nervous system, and symptoms can appear suddenly or within several hours, potentially causing severe illness or death. The marine toxins tend to accumulate in shellfish and dead fish rather than the water itself, although aerosolized toxins are also a risk, which can irritate eyes and lungs. When visiting the ocean, avoid swimming during advisories and prevent your dog from eating any kind of washed-up marine life.
By staying aware and taking precautions, you and your dog can enjoy the last licks of summer safely. As always, thank you for being a Riney Canine Health Center member, and we look forward to catching up with you next month!
Dr. Aly Cohen
Extension veterinarian
Cornell Richard P. Riney Canine Health Center
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