Officials warn about algae in Columbia

Clark County Public Health is warning residents of new dangers related to algae growths in local waterways. Benthic (that is, at the bottom of a body of water) algal mats found along the Columbia River have been linked to the death of two dogs.

“What we’ve talked about in Clark County for several years is planktonic algae blooms. We’ve been monitoring those in Clark County since 2007. These are the blooms that we see that are mixed into the water column. They collect in scums on the surface of the water,” Maggie Palomaki, environmental health specialist for the county, said during a Wednesday presentation to the Board of Health. “Benthic algae mats are a different type of harmful algae. We first tested these in Clark County in October 2024.”

Rather than being dispersed through the water column, Palomaki said, the algal mats attach to substrate at the bottom of the water. When there is an overgrowth of algae, the mats can detach and float to the surface.

“Since they are attached to the bottom of that body of water, they can appear in fast- or slow-moving water,” she said. “They also have a different texture. They’re very slimy, kind of gelatinous, slippery. So very distinct from the planktonic algae blooms.”

Palomaki said she received a call in October from a woman whose dog had died after being on Ackerman Island in the Columbia River near Camas.

“The dog had a very sudden onset of symptoms, including tremors, salivation, stumbling, vomiting, and then they died shortly after that at an emergency veterinarian’s office,” she told the council. “Fortunately for us, the vet recognized what might be happening and kept a stomach sample from that dog.”

In coordination between the Washington Department of Health and King County Environmental Lab, Palomaki said, the samples were tested and found to contain anatoxin-A and dihydroanatoxin, a toxin specifically associated with animal cases.

She said the dog’s owner also experienced symptoms of numbness and tingling of the mouth and tongue, likely from exposure while trying to resuscitate the dog.

After the pet owner reported the dog had mostly stayed on shore and away from the river, additional tests were done of plant matter found in the dog’s stomach. Those tests also showed high levels of cyanotoxins.

In August, a dog was reported to have died from exposure to cyanotoxins in St. Helens, Ore.

“We were not aware and had not received any reports of this type of algae in Clark County waters until this event happened in 2024. This is new to all of us,” Palomaki said. “Up to this point, our monitoring and education has been focused on the planktonic algae blooms that we see on the surface of the water. So we’re now asking ourselves, what can we do differently?”

Public Health has posted temporary educational signs at all 11 marinas and boat launches on the Columbia River and is creating new educational materials and more permanent signs specifically for benthic algae.

“We’ve also been adding that information to our website and updating our information map to include incidents related to benthic algae,” she said.

Anyone who suspects they or their pet have been exposed to benthic algae should call Clark County Public Health at 564-397-8428 or email [email protected].