AUSTIN (KXAN) — Austin’s popular park Red Bud Isle is closed effective immediately due to concerns about potentially toxic algae found in the water, according to the City of Austin.

The city sent out a warning Sunday after reports surfaced of two dogs dying after swimming in Lady Bird Lake.

City scientists examined the water Sunday after receiving those reports and found clumps of algae, especially near Red Bud Isle — 40% of the Red Bud Isle’s water surface is covered in blue-green algae.

The algae is being tested by the University of Texas and Texas A&M-Corpus Christi. Officials expect preliminary test results by Friday morning and full results on Monday.

Assistant City Manager Rey Arellano says officials cannot confirm that the dogs’ deaths are connected to the algae, but they are not disputing claims.

“Our information is anecdotal and we cannot confirm, but we have no reason to question the validity of these accounts,” Arellano said Wednesday.

Preliminary results indicate that this type of blue-green algae can release neurotoxins that can be harmful, and even deadly to pets. According to the city’s Watershed Protection Department’s assistant director Sarah Hartley, city scientists test Austin’s bodies of water nine time a year and haven’t seen this particular type of blue-green algae in Austin’s water before.

“This is a changing situation between climate change, between zebra mussels, things that are in our ecosystem that we may see change from time to time throughout the year, but also over the years,” Hartley said. “We’re going to continue to monitor and see how our lakes change due to those conditions.”

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.

The city is strongly advising pet owners to keep their pets out of the water.

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.

There are no known human deaths connected to blue-green algae. However, humans who come into contact with the water/algae at Lady Bird Lake could show symptoms like skin irritation, headache, fever, gastrointestinal issues, respiratory issues and neurological issues.