The death of a Portland dog hours after playing in the Willamette River has prompted state health and city parks officials to post warnings about the risks of toxic algae blooms.

Nutmeg, a rescue dog, was happiest playing ball. On Sept. 1, she played fetch at Sellwood Riverfront Park, running in and out of the river to retrieve her ball. She died within hours.

“She was just a sweet, sweet dog,” said her owner, Curtis Loeb, of Southeast Portland. “She was really affectionate.”

News of her sudden death spread quickly on social media after the rescue group that had arranged her adoption last year raised concerns about whether she had ingested dangerous toxins in the water while playing at the park. The group’s post has been shared more than 8,700 times on Facebook.

Cyanotoxins found in blue-green algae blooms can be harmful to humans and animals. Several dogs have died in Oregon over the past decade after drinking water contaminated with the harmful toxins. A blood test did not definitively conclude that Nutmeg died from cyanotoxin poisoning, Loeb said, but the veterinarian who treated her said she appeared to have ingested some sort of toxin.

Loeb hadn’t noticed anything unusual about the river, and Nutmeg did not wander off from the family. “The day we were at the river there were probably 100 dogs and that many people, too,” he said.

Officials at the Oregon Health Authority have not yet issued any public advisories related to Nutmeg’s death. Agency spokesman Robb Cowie said Sunday night that he was working to learn more information about the case.

Mark Ross, a spokesman for Portland Parks & Recreation, said state workers called the bureau Friday afternoon and asked the city to post signs at Sellwood Riverfront Park. Until then, no one at his agency had heard about Nutmeg’s death, he said. Although the city maintains the park next to the river, the state has jurisdiction over issues tied to the river itself, Ross said.

On Sunday afternoon, “dog safety alert” signs dotted the park and the shoreline. The signs explained the dangers of toxic algae in English and Spanish. They were laminated to withstand the rain that was pouring down. Two people and a dog walked along the river’s edge but never ventured into the water.

State and city officials are now discussing posting the signs at all parks that have access points to the river, Ross said.

Loeb, his wife, Megan Loeb, and their two children adopted Nutmeg through Oregon Weimaraner Rescue in October. They believe she was about 3 years old and resembled a German Shorthaired Pointer.

She loved to play, especially in water, and had been many times before to Sellwood Riverfront Park next to the Sellwood Bridge, Curtis Loeb said.

Sept. 1 was a warm and sunny Sunday, so he and his two children biked to the park with Nutmeg so she could exercise and cool off. After about two hours, Nutmeg started to slow down and looked tired. The family decided to leave and walked back with her toward their bikes.

“Nutmeg just started walking slower and slower,” Loeb said.

She struggled to walk, then to stand. She laid down on the grass. By that time, Loeb’s daughter had called his wife to pick them up so they could take Nutmeg to the vet.

“It was really strange because it happened so quickly,” he said. “It was just getting more and more apparent that she was in bad shape.”

The family lifted her into the vehicle and drove her to a nearby veterinary clinic. “By the time we got there she was just really out of it,” he said. “She just really did not look good. She was not very responsive at all.”

Nutmeg was breathing but her condition did not improve from any medical interventions. The veterinary staff noted that her legs were stiff and told the family she likely had a seizure, Loeb said.

He said the veterinarian told him that a blood draw did not conclusively point to cyanotoxins, but that Nutmeg’s symptoms indicated that she ingested some type of toxin in the water. It became clear she would not recover.

The Oregon Veterinary Medical Association issued a public warning about the dangers in 2013 after a dog suddenly died after swimming in water downstream from a Lane County reservoir.

“When in doubt, stay out,” they advised.

In 2009, Oregon State veterinary scientists confirmed that a Husky was killed by toxins found in blue-green algae after playing in Douglas County waters linked to at least three other canine deaths. The high number of deaths in the area has led state public health officials to issue a permanent advisory warning pet owners to avoid certain parts of the Lower Umpqua River.

Four other advisories remain in effect statewide, including one issued Sept. 3 for North Tenmile Lake in Coos County in southwestern Oregon.

Experts say water that appears foamy, scummy or off-colored, with green or red hues, may be contaminated by harmful algae and should be avoided.

Pets who come into contact with the water should be washed with clean water as soon as possible. If they swallow the water, they should be monitored for signs of illness such as weakness and dizziness. Pet owners who notice symptoms should seek veterinary care.

-- Molly Young

myoung@oregonian.com