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 occurred in 2020.

Current Status

April 22, 2022: Earlier this spring, we had observed a lot of green algae in the lake, but increased flows through the lake have reduced its presence. Especially as temperatures warm up, harmful algae may return at any time, or it may be present currently in pockets of slow-moving water on the lakes or in our creeks. People and pets should always avoid swimming in areas with algae or in water that is warm, stagnant, has scum or film. 

Watershed Protection has detected harmful algae on Lady Bird Lake, Lake Austin and Barton Creek in the past. LCRA has detected harmful on other Highland Lakes in 2021.

Green algae on Lady Bird Lake


Use our dashboards for algae testing results, water temperature and flow and nutrient levels in Lady Bird Lake and Lake Austin.

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.

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.
  • People and pets should not 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. 

Risk for People

Cylindrospermopsin, which was detected in the water of Barton Creek at Sculpture Falls, may cause liver and kidney damage. According to the EPA, acute human and animal health effects of exposure to this toxin include:

  • Fever
  • Headache
  • Vomiting
  • Bloody diarrhea

Seek medical treatment immediately if you believe you have been exposed. Please call 3-1-1 to report possible illness in people or pets from harmful algae.

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 or eating algae. Remember that people are not allowed to swim in Lady Bird Lake (Ord. 640611-C). 

Photo of brightly colored algae growing in a patch of Cabomba

In this photo from Friday, September 17, 2021, Cyanobacteria is showing up as brown, yellow and blue blobs among Cabomba plants.

Symptoms of Dihydroanatoxin Exposure

Dogs who ingest algae with dihydroanatoxin 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 paralysis

Bull Creek

The City was informed in early August that an individual became sick after playing in Bull Creek at Bull Creek Preserve. Watershed Protection tested algae and water samples and did not detect any toxins in the initial samples or the followup samples.

Testing and Monitoring

We will be monitoring three sites on Lake Austin and three sites on Lady Bird Lake, visiting them every other week throughout the summer. We will continue monitoring throughout the year, but may scale back the frequency as the year progresses. We will also begin monitoring one site on Lake Walter E. Long, visiting it at least three times during the summer and fall.

Map showing six monitoring sites on Lake Austin and Lady Bird Lake

Red dots indicate biweekly monitoring sites for harmful algae.

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. 

Algae at Red Bud Isle on October 14.

Algae at Red Bud Isle on October 14, 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.