A dog that went swimming in a New Brunswick river notorious for toxic algae has died, and animal welfare experts are warning pet owners of the risk.

The dog was playing in the St. John River in Fredericton when it began to vomit, according to a vet who treated the animal.

The dog’s owners rushed the animal to the vet, but it died shortly after arrival.

Veterinarian Dr. Colleen Bray said she believes that, because of the dog’s symptoms and the suddenness of its death, it likely came in contact with blue-green algae.

At least three dogs died last summer in the same river from the toxic algae blooms, which are particularly problematic in hot temperatures.

Samples have been sent to a lab to confirm the dog’s cause of death.

An animal protection group said the news is sad, but not surprising.

“We were sort of cautiously waiting, but hoping that this wouldn't happen,” said Andrea Boyd of Animal Crusaders of People For Stronger Protection. “So what we want to do and what Dr. Bray has thankfully done last night was put the message out there.”

The province issued a warning two weeks ago about the onset of blue-green algae.