When in doubt, stay out: How to keep pets safe from harmful algal blooms this summer

Algal blooms, or places in which algae has grown out of control, can happen all throughout the United States, in all kinds of water—freshwater, saltwater, and brackish. The good news is that often, blooms can be beneficial; in fact, according to the National Oceanic and Atmospheric Administration, algal blooms are the major source of energy for ocean food webs. Plus, they produce loads of oxygen.

That said, algal blooms can also be dangerous.

Karenia brevis, better known as “red tide,” occurs almost every year along the Gulf Coast of Florida, killing fish and marine mammals along with causing respiratory issues in humans. But the bloom grabbing current headlines is on the opposite end of the country in the Columbia River, which runs through Washington and Oregon, where exposure to a newly reported type of harmful algal bloom (HAB) has led to the death of two dogs.

Both deaths occurred in fall 2024, but with summer on the horizon, those stories are gaining traction now—and there are some important things veterinary teams should know, whether they’re based in the Pacific Northwest or anywhere else in the country.

The 411 on the new HAB

This new HAB is a benthic algae mat, explained Maggie Palomaki, an environmental health specialist with the Clark County (Washington) Recreational Water Safety team.

“While there are two known dog deaths on the Columbia River from exposure to harmful benthic algal mats in the area, there have been a handful of dog deaths over the years related to planktonic algae blooms, which we have been monitoring since 2007,” Palomaki said. “Planktonic algae blooms and benthic algae mats are both categories of cyanobacteria, often consist of similar species, and generally produce the same toxins. Benthic refers to the form and location the cyanobacteria growth occurs—in clumps/mats attached to a riverbed or lakebed—while planktonic algae grows in the water column and collects on the water’s surface in diffuse blooms.”

It was only last year that they first became aware of the harmful benthic algae in Clark County waters, she said, “and it’s not exactly known why this is the first time we are seeing it. Planktonic blooms have thrived with a warming climate, and it’s possible benthic algae is benefitting as well.”

Palomaki said that how widespread the benthic algal mats are still remains to be seen. “We are currently doing a media push to get the information out to the public, and as more people learn about benthic algae mats, it’s possible we will see more reports,” she said. “Not all species of cyanobacteria produce toxins, and ones that do are not producing toxins all the time so it’s very difficult to pin down. We know it’s in the Columbia River but have not yet evaluated other Clark County rivers.”

Pay attention to algae blooms

While nobody wants to employ scare tactics, this is a One Health issue that veterinary professionals—and the pet-loving public—must take seriously, as it impacts people, pets, and the planet.

“Honestly, the more I learn about harmful algal blooms, the more panicky I become,” said Lynn Healy, DVM, MS Natural Resources, president of Oregon VMA, and veterinarian at Cat Care Professionals in Lake Oswego, Oregon.

A big part of her concern stems from the fact that it can be really difficult for most people to identify whether algae in a body of water is harmful or not just by looking at it.

Palomaki shared this sentiment. “There are a variety of toxin-producing species, and they all present a little differently,” she said. “It is most commonly shades of green, brown, yellow, or red, [that] will grow attached to the substrate of the body of water and usually has a slimy or gelatinous texture.” She recommends the HAB photo guide from the California Water Quality Monitoring Council, which is what they use at Clark County; pages 12-24 cover planktonic blooms, and pages 25-36 focus on benthic mats.

Conditions for algae blooms

Still, understanding the conditions that benefit blooms is a good start.

Generally speaking, these algae love hot, nutrient-dense water. “So, areas where there’s sewage runoff, [or] agricultural runoffs where you hear about nitrates and phosphates getting into the water—those are nutrients that these algae love,” said Healy. “And they love stagnant or very slow-moving water. Those are kind of the trifecta that allow these things to bloom.”

What’s extra worrisome about these particular benthic mats, Healy said, is that they’ve been found in fast-moving water. Additionally, they adhere to the substrate at the bottom of the body of water, so they may not be dispersed throughout the water column in a way that one could visually notice. Plus, pieces can break off the mat and float elsewhere in the body of water, potentially impacting animals who step on it, swim through it, or drink near it elsewhere in that body of water.

While humans can be affected—especially children, who are more likely to put foreign objects in their mouths—it’s pets who are most at risk.

“What makes me very nervous is that situation where you really can’t tell what’s going to be harmful and what isn’t, and it can be minutes of a dog getting into the water, drinking the water [for the dog to be affected],” Healy said. “They love to drink water out of bodies of water, and they love to lick their fur after they’ve been in the water, and they love to eat grody stuff,” she said.

Healy, who works in a cat-only practice 90% of the time, noted that cats are a concern, too. “I see more and more videos of ‘adventure cats’ on social media—cats going on kayaks and paddle boards and boats,” she said. “Cats get very little mention in a lot of the information that’s out there about these algal blooms because it’s sort of assumed their risk of exposure is very low. But I sure am going to be letting my clients know that, if you’re one of those who takes your cat into the great outdoors, beware! A mammal is a mammal.”

An ounce of prevention

Both Palomaki and Healy agree that prevention is the number one goal.

“Education is key with preventing exposure, so vets willing to share information about harmful algae with their clients is extremely helpful, especially if they are in an area known to have harmful algae blooms or mats,” said Palomaki. “This could include having educational brochures on hand in the office, HAB posters hanging in exam rooms, posting information about harmful algae on their website or social media, etc.”

Healy’s simple mantra is, “When in doubt, stay out. Just don’t even get in the water. Don’t let your dog get near the water, because once they’ve ingested these toxins, it can be just minutes before they’re experiencing major clinical adverse effects. And by the time somebody realizes there’s a problem and get their pet to a veterinary clinic, it can be too late because there’s no antidote to these toxins.”

Symptoms vary based on which toxin an animal encountered, and those toxins vary by cyanobacteria species, said Palomaki. “Neurotoxins anatoxin-a and dihydroanatoxin-a are strongly associated with animal cases and produce symptoms such as stumbling, tremors, drooling, convulsions, trouble breathing, collapse, and sudden death,” she said. “The toxin microcystin, which are present in abundant quantities in planktonic blooms locally, affect the liver and generally produce GI symptoms such as vomiting, diarrhea, and stomach pain as well as lethargy and loss of appetite.”

If an animal presents symptoms of cyanotoxin exposure, Palomaki lists several things veterinarians can do to help health authorities:

Record the location of the animal’s recent whereabouts

Symptoms occur quickly (usually minutes-hours), and identifying the location of potential exposure is important for further testing or public notices.

If possible, collect and retain a stomach sample

Health authorities may be able to coordinate having the stomach contents tested for cyanotoxins.

Report it to the local health department

Health authorities only know about these cases if the owner or a vet notifies them.

Understanding treatment options

As for treating the affected animal, Healy notes that if the problem is identified in time, decontamination is the best bet.

“If somebody is with their pet at a body of water and they realize, ‘Oh, wait, maybe I shouldn’t have been letting my dog get into this water,’ they can go to a vet and get some decontamination,” she said. “That would be things like inducing vomiting [or] administering activated charcoal to try to prevent absorption of the toxins.”

However, once the clinical signs set in, like tremoring, incoordination, vomiting, diarrhea, excess salivation, and seizures, the pet may be too unstable to induce vomiting, so supportive care would be the only option. “And it can be days of supportive care,” Healy said. “Their livers can be permanently affected if it’s a hepatotoxin, and there are even coagulopathies that can occur and affect the heart. It’s bad news.”

Another step Healy urges veterinarians to take is to ask for a water recreation history in addition to a travel history for a sick pet—no matter where they currently are or where they’ve been. “It’s absolutely essential that, if it’s in those summer months—May to September—you have to ask the client, ‘Have you been recreating with your dog [or cat] near a body of water?’ And that can be standing water, a lake, a pond, a stream, or with these benthic mats, even more fast-moving water.”

Looking to the future and staying safe

The fact is, although authorities monitor and track HABs to the best of their ability, there are only so many resources available for this work—and there’s a lot of water to cover.

And, Palomaki added, “The science on managing harmful benthic algae is improving but still has significant gaps. There are a lot of resources for managing planktonic blooms, but those methods generally can’t be applied to benthic algae.”

“For example, alum products are often applied to lakes to bind phosphorous, starving the cyanobacteria of nutrients and preventing blooms,” she said. “Benthic algae, however, is known to survive in nutrient poor water and since it occurs in flowing water is constantly being supplied with fresh, untreated water.”

So, it remains vital that the public understand the dangers HABs pose to their pets, as well as what types of HABs are known to occur in areas where they plan to recreate near water. In regions with the types of HABs we’re used to, which tend to thrive in stagnant or slow moving water, identifying potentially problematic water sources is much easier—people can see the algae, or sometimes notice a rank or decaying odor.

However, in the Pacific Northwest—near the Columbia River, and potentially beyond—identification is far more challenging. Veterinary teams can do their part to help ensure pet owners are well-informed, and from there, it’s up to the families to weigh the risk of a day by the water. (And algal blooms or not, it’s always a good idea to adhere to basic water safety principles while out with pets in the summer!)

Further reading and additional resources

Palomaki shared a variety of helpful resources for those hoping to learn more about HABs—both in terms of how they impact animals and in general.

Animal-specific resources

• CDC Vet Reference Card
• CDC Vet HAB webpage
• CDC Animal HAB poster
• CDC Protecting Pets & Livestock
• Clark County Protect Your Pets brochure

Benthic-specific resources

• Clark County Public Health harmful algae mat brochure
• Clark County Public Health harmful algae mat postcard
• California Water Quality Monitoring Council on Toxic Algal Mats
• California Water Quality Monitoring Council HAB Photo ID Guide (planktonic blooms pg 12-24, benthic mats pg 25-36)

Photo credit: amriphoto via E+/Getty Images

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