Scientists with Austin's Watershed Protection Department have spotted clumps of blue-green algae near Red Bud Isle on Lady Bird Lake. This year marks one of the earliest seasonal reports of the algae, also known as cyanobacteria, which can be toxic to animals and humans.
Since it was first detected in the region in 2019, cyanobacteria has been a constant presence in Central Texas. Larger "mats" of the goopy-green algae typically appear floating in creeks or along lakeshores between late May and early August. According to a review of news reports, they've been detected in April only once before — in 2021.
Researchers say warmer-than-average weather and drought could be helping the algae grow this spring.
"It seems to correspond with low [water] flows [and] the warmer water temperatures," Brent Bellinger, conservation program supervisor with the Watershed Protection Department, said.
Bellinger said more sunlight also reaches into the water in the spring, since the tree canopy has not fully developed. Sunlight can stimulate algae growth.
A danger to dogs and swimmers
Over the last six years, cyanobacteria has killed several dogs that were exposed to its dangerous neurotoxins by swimming around it. In 2021, the city closed Barton Creek and Sculpture Falls after a human swimmer fell ill and toxins were detected.
The city had maintained an online "dashboard," now shut down, alerting the public about where the algae had been recently detected. But this year, officials say, you should assume the algae is always present in local waterways.
They urge people visiting lakes and creeks to avoid any high-risk areas where the water is warm or stagnant, or where algae is visible.
"We've been, in a sense, fortunate that the toxins have been contained within the mat material," Bellinger said. "So people can still recreate."
He said people and animals should stay away from the algae mats.
While Austin's Lady Bird Lake is a popular spot for boating and paddle boarding, swimming there is not allowed.
Cyanobacteria was first detected in Austin lakes after massive floods upstream brought runoff containing fertilizers and septic waste into the water. That injected a heavy dose of phosphorus into lakes and creeks, encouraging algae growth.
For the last four years, the city has treated sections of Lady Bird Lake with a modified clay to reduce phosphorus levels as part of a five-year pilot project to combat the algae. The pilot is entering its final year with mixed results.
Bellinger said the clay treatment may have reduced or slowed cyanobacteria growth in some areas, but it has not evicted the algae.
"The important thing is that we do still collect the cyanobacteria mats even after our treatments," he said, "and any mat could potentially be toxic and fatal to an animal."
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