Up until a few years ago, Austinites didn’t much worry about poisonous blue-green algae sickening them and killing their dogs. Then in 2018, flooding upstream of Austin sent massive amounts of runoff down the Colorado River and into area lakes.
That runoff contained agricultural and residential fertilizers, septic waste and other things that injected a supercharged dose of phosphorus into the water.
The algae, also known as cyanobacteria, feeds on phosphorous. So, its arrival in Lady Bird Lake the next year was likely not a coincidence, says Brent Bellinger, a senior scientist with Austin’s Watershed Protection Department.
Cyanobacteria is a dangerous neurotoxin. In 2019, it killed several dogs in Lady Bird Lake. It has since been detected in other lakes and, most recently, killed two dogs in Lake Travis last winter. In people, high exposure to cyanobacteria can cause muscle weakness, vomiting and liver damage.
“That has kind of thrown us for a loop,” Bellinger said. “We expect the bloom season to be mostly in the summer,” when waters are warmer.
Now, the City of Austin is planning something new to counter the algae: starving it of the phosphorus that helped it bloom.
As part of a pilot program, the Watershed Protection Department hopes to apply an “ionically modified clay” called Phoslock to 20 acres of lake surrounding Red Bud Isle this summer. Red Bud Isle, just downstream of the Tom Miller Dam, is where testing detected the highest levels of cyanobacteria in 2020.
Bellinger said the clay binds to phosphorus in the water. It then sinks to the bottom of the lake, where it is buried under other layers of sediment so cyanobacteria can’t reach it.
“We’re hoping to find that phosphorus and kind of starve [the cyanobacteria] from the bottom,” he said. “Hopefully, we don't have more large flood events that are just kind of recharging the system with excess nutrients.”
The pilot project will costs an estimated $300,000 and still needs final approval from Austin City Council.
As part of the project, Bellinger also plans on testing the effectiveness of floating filters containing activated charcoal against the algae by placing them on one side of Red Bud Isle.
He said he believes both approaches are environmentally safe and will only impact the areas directly treated. But they will not be a “silver bullet.”
Fully defeating the spread of cyanobacteria, Bellinger said, will require a regional approach to reducing phosphorus runoff into area lakes. But, he added, changing individual behavior can also help
“Whether it's putting in a rain garden, putting in a cistern, not fertilizing you lawn," he said, "All these things help.”
Got a tip? Email Mose Buchele at mbuchele@kut.org. Follow him on Twitter @mosebuchele.
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