So Is It Safe for My Dog to Swim in Austin This Summer?

City environmental scientist talks toxic algae forecast, mitigation

Dogs and people swim at Barking Springs in July of 2022 (Photo by John Anderson)

Since 2019, Austin's scourge of toxic algae has ebbed and flowed, terrorizing the dog-owning community. After suspicious but as-yet untested algae (which we should assume is toxic and avoid, the city says) was found at Red Bud Isle and Jessica Hollis Park March 10, the Chronicle asked Brent Bellinger, a senior environmental scientist for Austin Watershed Protection, for some advice on where the risk is highest this summer and what the city is doing to mitigate it.

"Any place in Austin carries some risk with it," he says. "The degree of that risk varies over time" and with the weather. After heavy rains like we had last week, which wash algae-producing nutrients like phosphorus and nitrogen into waterways, "it'd be advisable especially in the urban creeks to avoid any contact with the water for probably a good week, just to let bacteria levels settle back down."

Over the last few years, the city has found toxic cyanobacteria in almost every major waterway in Austin. At least five dogs have died as a result of ingesting the algae, and a person fell ill in 2021 after swimming at Sculpture Falls and ingesting the water. After that, the city implemented a five-year pilot for a mitigating product called PhosLock, meant to bury phosphorus and prevent it from contributing to algae production. That study has produced varying results, in places with varying sediment chemistry, possibly due to weather, says Bellinger: After August rains last year, PhosLock results at Festival Beach "were not what we had hoped for," but at Red Bud Isle, even without any applications of PhosLock over the dry winter of 2021, phosphorus remained pretty static.

One of the most concerning incidents happened last summer, when a dog died after swimming at Barking Springs. Could algae migrate over to Barton? After testing, Bellin­ger's team did find trace amounts of the toxin in the water, but well below the World Health Organization's recreational standards. This year, he says, they'll start monitoring a little earlier, to get a jump on collaborations with the Lower Colorado River Authority and the U.S. Geological Survey in studying the dynamics of the algal blooms. LCRA has been monitoring the Highland Lakes, and USGS will study why warmth-loving cyanobacteria has grown in cooler, groundwater-fed springs like Barton Springs: "This is something that's very under-studied globally ... looking more at the surface water-groundwater dynamics, and how those interact with the presence of toxic cyanobacteria at six sites around Austin." If things were to get really bad, says Bellinger, there are different options researchers are lab-testing: "Over the years, solicited or not, I've received treatment options from almost two dozen companies around the world."

This year's testing should yield preliminary results next month. In the meantime, Bellin­ger says, "There's no reason to avoid every single place around Austin out of fear. Most of the algae that's out there is benign, it's nontoxic. If there's no bad smells, you don't see any scums or sheens on the water, your risk is lower than a comparable spot that is stagnant, it's got a funky aroma – those would be places to avoid. Go to the Walsh boat ramp and let the dog jump into the water, but keep them away from the shoreline. You know, don't let the dog eat weird stuff. And it's fine."

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toxic algae, Brent Bellinger, Barton Springs, Barking Springs

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