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Toxic algae blooms expected to recur

Friday, August 23, 2019 by Jessi Devenyns

Algae in Austin’s waterways is nothing new. In the summertime when the water warms up and flows slowly, it’s common to see tendrils of blue-green algae floating in the current.

“It’s a very seasonal pattern. A very regular pattern,” Brent Bellinger with the Watershed Protection Department told the Environmental Commission at its Aug. 21 meeting.

This year, however, that seasonal algae became toxic, thanks to bacteria from the Oscillatoriales order.

Mateo Scoggins with Watershed Protection told the Austin Monitor that although this is the first summer these toxins have appeared, it may not be the last. “We’re going to plan that it is going to come back,” he said.

While the city cannot prevent the bacteria’s return, Scoggins said there are already plans to begin monitoring in the spring in order to preemptively warn the public. The department is also working to establish a safety threshold over which it is not safe for animals or humans to be in the water.

Although the exact species has not yet been identified, Bellinger said that the algae is producing anatoxin, a neurotoxin that caused the death of three dogs earlier this month after they swam in the lake.

There have not been any more fatal incidents due to the algae, but the Watershed Protection Department is continuing to monitor Auditorium Shores, Red Bud Isle and Barton Creek near Lady Bird Lake, as well as other bodies of water, including Walter E. Long Lake, twice weekly.

While the city will be monitoring bacteria levels in the algae for the foreseeable future, Scoggins is confident that the algae will have cleared up by late September or October. Warning signs remain posted along Lady Bird Lake, although entering the water is not prohibited.

“We believe that the water is completely safe for people … (but) we want to be cautious,” said Sara Hartley, assistant director of the Watershed Protection Department.

As for why the algae developed toxins this year, Bellinger told the commissioners that the department has “a couple of working hypotheses,” including the invasion of zebra mussels last year, flood events that increased sediment concentrations, fecal matter and climate change. All the theories boil down to increasing the nutrient density in the water, which is a prerequisite for harmful algal blooms. And – except for dog excrement, which is a perennial problem – all are conditions that were new to the water systems this year and may have altered the development of the seasonal algae growth.

According to Bellinger, not all cyanobacteria in algae can produce toxins and even those that can need to be activated by the right set of environmental circumstances, including increased nutrient density in the water, to produce harmful effects.

Fortunately, the toxicity is not a threat to aquatic life. Bellinger explained that the bacteria that produce these harmful chemicals are akin to a “kidney bean” in the food chain when the creatures that inhabit the water are actually in the mood for “steak,” and as a result, they are not consumed for fuel.

Future occurrences of this toxic algae remain uncertain. But Bellinger says at least “now we know we have a new boogeyman to look out for.”

Photo by Cesar Garza made available through a Creative Commons license.

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