Symptoms and Reporting Suspected Illness

If you, a family member or pet have sudden, unexplained symptoms after swimming, contact your medical provider, veterinarian or the Texas Poison Control Center at 1-800-222-1222. Please also let us know by completing our form:

Resources for physicians

Resources for veterinarians

You can find information on symptoms on the Centers for Disease Control and Prevention's website, Illness and Symptoms: Cyanobacteria in Fresh Water.

Caution: Enter Water at Your Own Risk

There is always some level of risk in a natural water body. In addition to algae, bacteria, parasites and other dangers may be present.

People and Pets

  • Do not drink water directly from natural water bodies.
  • Avoid contact with algae.
  • Rinse skin or animal fur after contact with water.
  • Do not allow dogs to lick their fur prior to rinsing.

Do Not Enter Water a Natural Water Body If:

  • Water is warm or stagnant or you see scum, film or algae.
  • There has been rain in the past three days.
  • There are lots of dogs present.

Note that people are not allowed to swim in Lady Bird Lake (Ord. 640611-C). 

Toxins and Previous Results

The list below shows the toxins that we have detected in algae and/or water since 2019. In most cases, the toxins were contained in the algae and not released into the water. Symptoms of exposure depend on the type of toxin, how the exposure occurred and how long the exposure lasted. See “Additional Resources” below.

  • Anatoxin-A
  • Cylindrospermopsin
  • Dihydroanatoxin-A
  • Homoanatoxin-A
  • Saxitoxin

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. 

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

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.

FAQs About Harmful Cyanobacterial Algal Blooms & Drinking Water

What are cyanobacteria?

Cyanobacteria, also called blue-green algae, are microscopic organisms found naturally in all types of water. These organisms use sunlight to make their own food. In warm, nutrient-rich waters, cyanobacteria can multiply quickly, creating algal blooms that spread across the water’s surface.

Two types of harmful algal blooms are planktonic and benthic proliferations. Planktonic are free-floating microscopic cells that are suspended in the water column or float as scum on the water surface. Benthic algae originate on the bottom of lakes in shallow water. Benthic mats can remain on the bottom of the lake or float to the surface. Austin Water monitors the water entering our treatment plants for both types of harmful algae.

How are cyanobacterial algal blooms formed?

Cyanobacterial blooms form when cyanobacteria start to multiply very quickly. Blooms can form in warm, slow-moving waters that are rich in nutrients from sources such as fertilizer runoff or septic tank overflows. Cyanobacterial blooms generally need an abundance of nutrients to grow. The blooms can form at any time, but most often form in late summer or early fall. Algal blooms and cyanobacteria are monitored closely by Austin Water’s Water Quality Lab, as well as the City of Austin’s Watershed Protection Department and the Lower Colorado River Authority.

Why are some cyanobacterial algal blooms harmful?

Harmful cyanobacterial algal blooms may affect people, animals, or the environment in the following ways:

  • Some cyanobacteria in algal blooms may produce toxins called cyanotoxins that can make people and their pets sick. Those experiencing symptoms should consult a physician right away.
  • The blooms can block or reduce the sunlight that other organisms need to live.
  • They use up nutrients that other organisms need to live.
  • They use up the oxygen in the water as they die down, which can kill fish and other aquatic life.

How do cyanotoxins affect drinking water quality?

Cyanobacterial algal blooms that create cyanotoxins can occur Lake Austin and Lake Travis, which supply drinking water for Austin. Winds and water currents can transport algal blooms near drinking water intakes at water treatment plants. If cyanotoxins enter the drinking water treatment plant and are not removed during treatment, people can be exposed to cyanotoxins through their tap water. Cyanobacteria may produce taste and odor compounds that could cause problems in drinking water.

Is there testing for algae and cyanotoxins in water?

There are no national or state requirements for monitoring cyanotoxins. While algal blooms may contain cyanobacteria that have the potential to release cyanotoxins, these harmful toxins may not actually be present in the water itself.

Austin Water conducts routine testing for the presence of cyanotoxins in both raw lake water taken from Lake Austin and Lake Travis, as well as in water that has finished the treatment process at the Handcox, Davis, and Ullrich Treatment Plants. Tests for the presence of phytoplankton (microscopic algae) and cyanotoxins in raw lake water are conducted on a bi-weekly basis. The sampling frequency may be adjusted based on changing conditions. Current tests are non-detect for cyanotoxins in raw or treated drinking water.

Additionally, Austin Water uses several processes in treatment plants which are effective in removing cyanobacteria and cyanotoxins. The harmful cells containing the toxins can be physically removed through the coagulation, flocculation, sedimentation, and filtration process. Chlorine, which is part of the plant’s disinfection process, is destructive to cyanotoxins. Finally, the powdered activated carbon that is used to remove taste and odor-causing compounds also removes cyanotoxins.

How can I help reduce cyanobacterial harmful algal blooms from forming?

Reducing nutrient pollution, such as excess nitrogen and phosphorus, is essential to reducing the formation of cyanobacterial blooms. Excess nutrients may originate from agricultural, industrial, and urban sources as well as from atmospheric deposition. Things you can do to reduce nutrients in your local waterways include:

  • Use only the recommended amounts of fertilizers on your yard and gardens to reduce the amount that runs off into the environment.
  • Properly maintain your household septic system.
  • Maintain a buffer of natural vegetation around ponds and lakes to filter incoming water.
    • Stop fertilizing within 20 feet of lakes, rivers, and ponds.
    • Plant natural vegetation around ponds and lakes to filter incoming water.
  • Do not add fertilizers when the ground is frozen.
  • Do not apply fertilizer immediately before or during rain and snow.

For more information on cyanobacterial blooms and cyanotoxins, please visit:

Resources for the public