Watershed Protection is conducting a five-year pilot program, using lanthanum-modified bentonite to reduce the amount of phosphorus available to Cyanobacteria, or blue-green algae, in Lady Bird Lake. Reducing phosphorus levels may help prevent the growth of harmful algae. Lanthanum-modified bentonite is safe, but boaters should still keep plenty of distance from the barge during applications.
2024 is the fourth year of this program. The results since 2021 have been mixed.
Dates for 2024
- Monday, June 3, - Tuesday, June 4
- July 8
- August date to be determined
Locations for 2024
- Red Bud Isle
- The boat ramp on the north shore of the lake, just west of I-35.
- The north shore of the lake between I-35 and the lagoon behind the Festival Beach Boat Ramp.
The second location is new and has been chosen for research purposes to help identify any unforeseen impacts on aquatic insects. No impacts are expected.
Results from 2021 to 2023: Red Bud Isle
At Red Bud Isle, there has been a reduction in the amount of harmful algae after each application in June. The 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.
Results from 2022 and 2023: East of I-35
The lanthanum-modified clay does not appear to be having any effect in this area, which includes the area from the north shore to the middle of Lady Bird Lake, between I-35 and the lagoon near the Festival Beach boat ramp. We did not apply the material on the other side of the lake along the south shore to allow us to compare the two areas. There was almost no difference in the available phosphorus between the two areas. This may be because new sediments from upstream are bringing in more nutrients.
How Lanthanum-Modified Bentonite Works
Lanthanum-modified bentonite consists of a modified clay material. It is widely used to prevent harmful algae blooms, which are more likely in warm, stagnant water with high nutrient levels. Lanthanum-modified bentonite binds to phosphorus, a key source of nutrients for algae. Once bound into a mineral form, the phosphorus becomes unavailable to the algae. The idea is to rob the algae of one of its primary food sources and reduce its growth.
Budget
- $300,000 per year for five years (2021-2025)
- Includes material, application and monitoring of sediments