City-Contracted Toxic Algae Mitigation Tactic Has Seen “Mixed” Results

Dogs and people at Barkin’ Springs (photo by Jana Birchum)

Besides mounting heat, for the last few summers, Austinites have had to deal with another danger: toxic algae. Since 2019, at least five dogs have died as a result of ingesting toxins in Lady Bird Lake, and toxic algae has been found every year since at Red Bud Isle and Festival Beach, as well as around the Highland Lakes and Barton Creek.

On July 5, the Lower Colorado River Authority reported a dog had died after swimming at Point Venture on Lake Travis, but after testing the water, LCRA didn’t detect any toxins. They did, however, find algae in a nearby cove, and are still urging that “people and pets avoid all contact with algae in the Highland Lakes,” as it can begin producing toxins at any time “without a change in appearance.”

The city is now in its fourth year of a contract with the company EutroPHIX to test a mitigation tactic that stops algae from spreading. EutroSORB G’s clay binding agent buries phosphorus, the nutrient that, in excess, leads to algae production. This summer, the city has so far applied it at Red Bud Isle, the boat ramp on the north shore of the lake, and at the north shore of the lake between I-35 and the lagoon behind the Festival Beach Boat Ramp – that last location is new, to test any unwanted impacts on aquatic wildlife, though none is expected.

Based on preliminary findings this year, Red Bud Isle has seen the most progress, with “very little phosphorus in a form available for blue-green algae to use,” says the Watershed Protection Department’s Stephanie Lott. At Festival Beach, “more of that phosphorus is becoming unavailable.” Basically, there’s fewer nutrients to feed toxic algae growth.

However, the city said in May that “the results of the pilot program over the past three years have been mixed.” There is a consistent reduction in algae after each application in June, but July and August applications “appear to hold the line without achieving any further reduction of the algae. By the time following June and the first application of the year rolls around, the algae has generally returned.” Plus, the treatment doesn’t appear to be having any effect east of I-35. The city says this could be “because new sediments from upstream areas” – outside the city’s jurisdiction – “are covering up the clay and bringing in more nutrients.”

West Bishop, an aquatic scientist at EutroPHIX, agrees, explaining it as “like treating weeds in only one part of your yard; the untreated sections continue to contribute to the overall problem.” Bishop says though the ultimate goal is to eliminate algae altogether, mitigation has been working, and “we intend to use what we have learned to inform a more comprehensive treatment approach across the entire system in the future for sustained results.”

The pilot costs $300,000 per year, funded through your utility bill’s drainage charge, so the city urges Austinites to do their part to by reducing fertilizer usage to mitigate the amount of bad nutrients flowing into the lake, and for homes located along creeks, replacing lawns with trees and native grasses helps reduce runoff. The city says that “reducing the amount of nutrients being washed into the lake would likely be the most effective solution.”

Editor's Note Monday, July 29, 4:15pm: This story previously referenced the product Phoslock; that is no longer in use, and has been replaced by EutroSORB G. The Chronicle regrets the error.