A harmful algae bloom occurs when cyanobacteria, also called blue-green algae, produce toxins. Lady Bird Lake experienced a harmful algae bloom in 2019, which sickened and killed several dogs. Another one has occurred in 2020.

Current Status

April 6, 2021 – We have detected low levels of dihydroanatoxin in an algae sample taken in mid-March from Lake Austin near Mansfield Dam. Trace levels were also detected in two algae samples from Lady Bird Lake. This is the same toxin that LCRA has detected in other Highland Lakes earlier this year and the same one found in 2019 and 2020 in Lady Bird Lake. Although levels of the toxin are low, they indicate an increased risk for dogs in the water bodies.

At this time, we are recommending that dog owners not allow their dogs to ingest or touch algae in any area lakes, creeks or water bodies. People should also avoid the algae. 

The risk may also be elevated at stock ponds or stormwater ponds. Although these ponds may be attractive, their water quality tends to be poor and is not suitable for recreation at any time for either people or pets.

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Lady Bird Lake continues to meet State of Texas contact recreation standards, which are based on bacteria levels. 


There is always some level of risk in a natural water body. There is currently an increased risk in Austin's waterways.

  • Avoid stagnant areas or areas with algae.
  • Do not allow dogs to touch or ingest algae.
  • Rinse your dog after contact with the water.
  • If your dog becomes sick after swimming, take your dog to a veterinarian immediately.

If you allow your dog to swim, you do so at your own risk. 

Symptoms of Exposure

Dogs who ingest algae with this toxin could have a number of symptoms, including respiratory paralysis and death. Dogs can also be exposed to the toxin by licking algae from their fur. Look for these signs in your pet within minutes to hours of exposure:

  •     Excessive drooling, vomiting and diarrhea
  •     Foaming at the mouth
  •     Jaundice and hepatomegaly
  •     Blood in urine or dark urine
  •     Stumbling
  •     Loss of appetite
  •     Photosensitization in recovering animals
  •     Abdominal tenderness
  •     Progression of muscle twitches
  •     Respiratory paalysis

Risk for People

The risk to humans is currently low. The 2019 harmful algae bloom appears to have only affected dogs. The toxins were contained in the algae and not released into the water. It is always recommended that people avoid stagnant areas of the lake and handling algae. Remember that people are not allowed to swim in Lady Bird Lake (Ord. 640611-C). 

Testing and Monitoring

Given that the toxins have been detected during the cooler season and in at least four lakes, the Watershed Protection Department plans to reevaluate its monitoring program. 

Algae at Red Bud Isle on October 14.

Algae at Red Bud Isle on October 14, 2019.

Cause and Type of Algae

Blue-green algae are one of the earliest forms of life and are common worldwide. Keep in mind:

  • There are many types of blue-green algae, but only some species can produce toxins. 
  • There are several different types of toxins possible. 
  • Even if a species is capable of producing toxins, that doesn't mean it will always do so. Generally, harmful algae need warm water, low flow and high levels of nutrients.  

Blue-green algae can be single cells spread throughout the water. When they form mats that are big enough to see, they usually look like dark green, slimy blobs. Mats can be on the bottom or floating on the top of the water. Blue-green algae are often mixed in with other types of algae.  

We are not aware of any human or pet health problems from harmful algae in Austin prior to 2019. Zebra mussels, flooding during the fall of 2018 and climate change are potential contributing factors to the harmful algae bloom in 2019. 

Drinking Water

Austin Water regularly tests algae levels on Lake Austin and Lake Travis near their intake pipes and has not seen levels of concern for drinking water. Currently, Austin Water does not use Lady Bird Lake as a source for drinking water.

Other Bodies of Water

Stock ponds and stormwater ponds have the highest risk for harmful algae. Most are privately owned. Although these ponds may be attractive, their water quality tends to be poor and is not suitable for recreation at any time for either people or pets. 

We recommend avoiding water bodies that are warm and stagnant at any time.