A New Brunswick veterinarian suspects blue-green algae killed a dog playing in the St. John River.

Dr. Colleen Bray at the Douglas Animal Hospital says the dog was swimming in the river and started to vomit.

The owners immediately called her office, but the animal died before they arrived.

Because of the symptoms, and how quick it all happened, she believes the dog came in contact with blue-green algae. The toxic blooms can be found along the banks of the river, especially when it’s hot and the water is stagnant.

“We don’t have any testing back, but the pattern of: very hot weather, actively swimming in the water during the hot weather, the symptoms that the dog presented with and the rapid onset of death all fit with a strong possibility of blue-green algae toxicity,” Bray said. “Because of that, I just wanted pet owners to be aware that there’s a strong possibility and keep their pets out of the water until we know more.”

An animal protection group is asking the same.

“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.”

Whether or not the dog did die from the blue-green algae has to be proven.

Samples have been sent for testing at a provincial lab.

The algae was responsible for three dog deaths last summer in New Brunswick.

The province's public health put out an advisory two weeks ago, warning people that the algae could be back.

New Brunswick's chief medical officer of health issued an advisory on June 27 warning people to check bodies of water and shorelines for the algae that often blooms in warm weather.

Dr. Cristin Muecke, the province's deputy chief medical officer of health, said Monday that people should check recreational water before entering.

"If you see anything or smell anything unusual, it's best not to go in the water. We recommend that you don't swallow recreational water. You should rinse after getting out, and don't go in if you have any open cuts or sores," she said.

Muecke said there's no greater concern about the St. John River than any other body of water in the province.

"You can also check our website to ensure if there have been any previous experiences with blue-green algae in that water body," she said.

Not all blue-green algae blooms are toxic, but experts advise treating all blooms as if they are. Bray said symptoms, which also include salivation and signs of neurological change, can materialize with an otherwise healthy animal within 10 minutes of entering water.

Jim Goltz, manager of New Brunswick's veterinarian laboratory service, said the algae can sometimes can appear brown, different shades of green or even red.

Goltz said there are a few things you can do to ensure dogs stay healthy at the beach.

"Make sure your dog is well hydrated before you go to the beach. Give it nice clean water in a clean bowl and make sure that it drinks that water well so that it's not thirsty before going around the water," Goltz said.

"It's also important to keep dogs under strict supervision when they are with you at the beach. Make sure they don't eat mats of vegetation. Those mats can often concentrate toxins of algae," he said.

Muecke said adults or children exposed to the toxic algae can also become ill.

"If exposed to blue-green algae you could get skin, throat or eye irritation. That might last a couple of days. If you ingest the water you may experience gastrointestinal symptoms," she said.

The dog that died Saturday entered the water from an island in the river in the Fredericton area. Goltz said a crew will examine the area.

With files from CTV Atlantic’s Laura Brown and The Canadian Press.