AUSTIN (KXAN) — The city of Austin is warning pet owners to keep their animals from swimming in and drinking out of Lady Bird Lake.

The city is sending out the warning after reports of two dogs dying after swimming in Lady Bird Lake. While the city can’t confirm the dogs’ causes of death, city scientists examined the water after receiving those reports and found an abundance of algae, especially near Red Bud Isle.

Nearly 40 percent of the water around Red Bud Isle is covered in algae, they say. According to the city’s Watershed Protection Department, preliminary tests indicate the algae is a type of blue-green algae.

Blue-green algae can release a neurotoxin that is harmful to people and animals. City officials say while Austin waters have had some blue-green algae in the past, they are not aware of any that ever released neurotoxins.

City officials expect to have test results that will show whether the algae is toxic by next week.

Austin Water does not use Lady Bird Lake as a source for drinking water and city staff does not believe the algae are impacting drinkable water in Austin.

Dogs that ingest water contaminated with the toxin found in blue-green algae could have a number of symptoms that show up within minutes or hours of exposure. Those symptoms include excessive drooling, foaming at the mouth, vomiting, diarrhea, stumbling, muscle twitches and respiratory paralysis. Dogs that are exposed can die from the toxin.

Claire Saccardi is one of the pet owners who reported her dog’s death to the city. She took her four-year-old Golden Retriever, Harper, to Red Bud Isle on Thursday. Within about an hour and a half of leaving, Saccardi says Harper began showing symptoms.

“All of the sudden, she started walking down a step and she collapsed,” Saccardi said. “Both of her front legs stopped working. She couldn’t stand up. She looked at me with the saddest little puppy eyes.”

Saccardo says Harper then began shaking with tremors.

“She’s struggling to breathe, and she starts getting a little foam in her mouth, and so we take her to the emergency vet, and ten minutes after we got there, they told me that, ‘Your baby’s not doing good. We have to give her CPR,’ and she died shortly after that.”

Saccardi’s medical records show the emergency veterinarian who treated her listed blue-green algae intoxication as a suspected cause of death.

“Until we have more information, we strongly advise that pets stay out of the water,” a spokeswoman for the city’s Watershed Protection Department wrote in a statement. “At this time, we have no reason to believe that boating is unsafe. However, people should not be swimming in Lady Bird Lake. It is illegal. When out on the lake, people should take care to avoid ingesting water or coming into direct contact with the algae. The degree of risk to human exposure, such as through accidental swallowing of lake water, cannot be known until the tests results are available and analyzed.”

Once the results from toxicity tests are available, they are expected to be released.

Scientists have linked the presence of zebra mussels to blue-green algae blooms in the Great Lakes. Researchers say they eat “good algae,” but release blue-green algae back into the water.