Wednesday, May 17, 2023

As weather heats up, so does the risk of toxic algae


Blue-green algae are present at most monitoring sites on Lady Bird Lake and Lake Austin 

The City of Austin has resumed monitoring and testing cyanobacteria, also called blue-green algae. Certain species of blue-green algae can produce toxins, which are potentially harmful to people and pets. During initial visits this year between May 2 and May 12, staff found blue-green algae at all monitoring sites on Lady Bird Lake and Lake Austin, except for Walsh Boat Landing. Please assume that the algae may be toxic. 

We recommend that people and pets avoid contact with algae, not drink water directly from the lake, and rinse off after contact with the water. Do not allow dogs to lick their fur prior to rinsing. Please note that swimming is prohibited in Lady Bird Lake. 

Our routine algae monitoring program includes biweekly visits to Lady Bird Lake and Lake Austin during the summer and early fall. If blue-green algae are present at a site, staff take samples of algae and water and send them to a lab for analysis. The program is paused over the winter and spring when algae growth is reduced. This allows staff time to process data.  

Analyzing the algae for toxins takes time. The tests are unusual, complex and not readily available. They are being done at university labs for research purposes. Results will be posted at as soon as they are available. We anticipate the lab results being available in June. 

The monitoring program provides a snapshot of conditions at specific locations at the time samples were taken. It is the most current data we have to evaluate the extent of harmful algae on our lakes, but is not suitable for determining the safety of a particular area on a particular day for recreational use.  

We are not currently monitoring creeks for harmful algae, but it could be present. Bacteria, such as E.-coli, parasites and other dangers may also be present. We recommend not getting in the water if it is warm, stagnant or if you see scum, film or algae. Due to the risk of bacteria, you should also avoid natural water bodies for at least three days after it rains and if lots of dogs are present.   

If a person has sudden, unexplained symptoms after swimming, they should contact their medical provider or the Texas Poison Control Center at 1-800-222-1222. For a pet, they should contact their veterinarian. Please also let us know by completing the reporting form, found at  

To try to reduce the amount of harmful algae present on Lady Bird Lake, we will continue our pilot program and apply lanthanum-modified clay at Red Bud Isle and east of I-35, starting in late June. This product helps reduce the phosphorus available for algae growth. Over the past two years, we have seen a drop in nutrient levels and the amount and toxicity of blue-green algae near Red Bud Isle. However, last year we did not see the same success east of I-35. This may have been due to rainfall and increased flows through the lake following the applications.  

On Lady Bird Lake, we have documented harmful algae proliferations every year since 2019, when several dogs died after swimming in the lake. On Lake Austin, algae sampling began in 2020, and harmful algae has been detected on that lake every year since then.  

It is possible for the toxins to be released into the water, but that has not been detected on Lady Bird Lake or Lake Austin. Instead, the toxins have been contained in the algae itself. This means that exposure to the toxins occurs through ingestion or contact with the algae. 

There is more information at

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