Watershed Protection will be treating two areas of Lady Bird Lake in 2022 with Phoslock. Last year, Phoslock treatment successfully reduced the amount of phosphorus available to algae in the treatment area. Reducing phosphorus levels may help prevent the growth of harmful algae.

Although Phoslock is safe for humans, the environment and wildlife, we ask that boaters keep plenty of distance from the barge applying Phoslock during treatments.

Video about Phoslock Treatments

Treatment East of I-35

  • Amount: 30,000 pounds of Phoslock per treatment
  • First Treatment: Monday, June 13, and Wednesday, June 15, 2022.
  • Second Treatment: July 18 and 19
  • Third Treatment: August 15 and 16
  • Area: From the north shore to the middle of Lady Bird Lake, between I-35 and the lagoon near the Festival Beach boat ramp.

Please note that we will not treat the south shore in this area. The south shore will act as a control area to help evaluate the effectiveness of the treatment. This area of the lake was chosen for treatment due to the presence of harmful algae with multiple toxins in 2021.

Treatment at Red Bud Isle

  • Amount: 30,000 pounds of Phoslock
  • First Treatment: Tuesday, June 14
  • Second Treatment: July 18 and 19
  • Third Treatment: August 15 and 16

Background

Watershed Protection conducted a pilot project in 2021 to try preventing the growth of harmful algae near Red Bud Isle. We tested whether Phoslock treatments and biochar would reduce nutrient levels and the amount and/or toxicity of blue-green algae in the pilot project area. 

We applied 120,000 pounds of Phoslock over 22 acres of Lady Bird Lake near Red Bud Isle. There were three applications in June, July and August. Sediment testing showed a significant decline in the amount of phosphorus available to blue-green algae. Sediment testing in May 2022 continued to show the same great results.

How Phoslock Works

Harmful algae thrive in warm, stagnant water with high nutrient levels. Phoslock binds phosphorus, a key nutrient, so that it is unavailable to the algae.   

Graphic showing how Phoslock binds to phosphorus and sinks to the bottom of the waterbody.

Initial chemical analysis in June 2021 showed about 40% of the phosphorus in the water around Red Bud Isle was mobile and available as a food source to blue green algae, as represented by the blue circles in the graphic. After the Phoslock treatment, the amount of mobile phosphorus declined to 18%, a significant decrease. Sediment testing in May 2022 continued to show the same great results.

Safety Information

Phoslock is safe for humans, the environment and wildlife. It is a patented technology and consists of a lanthanum modified bentonite clay material. It was specifically developed to bind phosphorus in surface water and sediment and has been widely used to prevent harmful algae blooms. 

Over 80 peer-reviewed publications exist on Phoslock that specifically address its efficacy, longevity and potential impacts. Phoslock has received U.S. and Canadian NSF/ANSI Standard 60 Certification for use in drinking water.

Budget

  • $300,000 per year for five years (2021-2025)
  • Includes treatment and monitoring of sediments