Beware of Blue-Green Algae in Lakes Across the US 

Beware of Blue-Green Algae in Lakes Across the US

Keep Your Dog Safe and Enjoy Your Summer Outings

Freshwater algae and cyanobacteria

Freshwater algae play an important role in aquatic ecosystems. Most algae are harmless, but some species (notably cyanobacteria, also called blue-green algae) can on occasion produce toxins that can be dangerous to animals and people. These events are known as harmful algal blooms, or HABs, when they occur suspended in the water column. When these events occur as algal mats, they are referred to as harmful algal proliferations, or HAPs.

Current harmful algae status in the Highland Lakes

LCRA regularly monitors water samples for cyanotoxins in lakes Buchanan, Inks, LBJ, Marble Falls, Travis, Bastrop and Fayette.

In the summer of 2023, LCRA began testing algal material in Lake LBJ and Inks Lake as part of a joint study with the City of Austin. Testing from July, August and September 2023 detected high concentrations of toxicity in algae tested from three sites on Lake LBJ and three sites on Inks Lake. LCRA will post results from additional testing on their webpage as they become available.

The City of Austin monitors for toxic algae in Lake Austin, Lady Bird Lake and Lake Walter E. Long. For more information on City of Austin cyanotoxin monitoring, visit

LCRA strongly recommends avoiding all contact with algae and treating all algae as if it could be toxic, regardless of whether testing has detected any cyanotoxins in the area. Algae can begin producing toxins without warning or change in appearance.

Blue-green algae

Blue-green algae or cyanobacteria naturally occur in water bodies throughout Texas, including those in the lower Colorado River basin. Algae can occur year-round, but they typically thrive during the hot summer months. On occasion, blue-green algae can produce toxins that can be harmful to people and pets. Algae that are producing toxins are called harmful algal blooms (HABs) when suspended in the water column and harmful algal proliferations (HAPs) when the algae form mats.

It is impossible to tell whether blue-green algae are producing toxins by look, touch or smell, so scientific testing is required to determine if toxins are present. Though it is difficult to predict precisely when or if blue-green algae will produce toxins, toxin production in general is usually triggered when environmental conditions include excess nutrients (nitrogen and phosphorus); warm water temperatures; calm, stagnant or low-flow conditions; and ample sunlight. Harmful algae may only last a few hours or can persist for several weeks depending on weather conditions and characteristics of the waterbody.

The name blue-green algae can be somewhat misleading in the identification of cyanobacteria. Blue-green algae are most commonly blue/green, dark green, brown and black. They can make water appear as swirls of green paint, green pea soup or floating mats of what may look like moss or scum. Blue-green algae can also be intermixed with other algae that do not produce toxins (i.e., green algae and diatoms).

Exposure to harmful algae

People and pets can be exposed to harmful algae toxins through direct skin contact from swimming and other recreational activities or ingesting water or food contaminated with harmful algae toxins.

Harmful algae toxins can cause skin and eye irritation or rashes. Severe reactions can occur when large amounts of water are ingested, and can range from diarrhea, cramps and vomiting to fainting, dizziness and numbness, or tingling in lips, fingers and toes. If you think you are experiencing symptoms related to exposure to harmful algae toxins, call your doctor or a poison control center immediately. For more information, visit the Centers for Disease Control and Prevention HAB-Associated Illness webpage.

Dogs are primarily at risk through ingestion. Dogs’ behaviors such as picking up items from a lake in their mouth or licking their fur after swimming through algae can put them at a high risk for exposure to harmful algae. The best way to protect you and your pets from toxins is to avoid all direct contact with algae.

Animals can experience symptoms within minutes of exposure to toxicity, including drooling, rashes, vomiting, diarrhea, weakness, difficulty breathing, loss of energy and appetite, stumbling and falling, foaming at the mouth, seizures, and even death.

Report a dog illness that may be related to toxic algae in the Highland Lakes to LCRA by emailing Contact LCRA. Include information about your dog (breed and size), when and where the dog may have been exposed, the dog’s symptoms and your contact information.

Drinking water supplies
Utility operators are responsible for testing and treatment to remove harmful algae toxins to meet federal regulatory guideline limits for public water supply uses.

Risk of exposure from swimming

Natural bodies of water are not chlorinated or disinfected, so there is always a risk of contact with bacteria or other toxins when swimming in the Highland Lakes. Water quality conditions can change frequently and can vary from one part of a lake to another.

Humans, pets and livestock that interact with harmful algae toxins either through physical contact or ingestion can become sick, or in extreme cases, become paralyzed or die. People who enter the water do so at their own risk.

To keep pets safe while swimming in the Highland Lakes:

  • Avoid areas with algae or that are stagnant.
  • Don’t let dogs consume lake water, algal material or other shoreline debris.
  • Don’t let dogs lick their fur or paws after getting out of the water.
  • Rinse your dog after contact with lake water.
  • Provide clean, fresh water for drinking.
  • If your dog becomes sick after swimming, take your dog to a veterinarian immediately.

Help minimize growth and spread of harmful algae

Once harmful algae appears, there are few options besides letting it run its natural course. Chemical treatment methods such as algaecides approved by the U.S. Environmental Protection Agency and Texas Department of Agriculture are not recommended during a bloom or proliferation and can contribute to a temporary reduction in water quality in the form of low dissolved oxygen levels and the release of algal toxins from dying algal cells.

Land use has a direct effect on water quality, and water quality is directly related to harmful algae growth and abundance. To help reduce man-made sources of nutrients:

  • Pick up and properly dispose of pet waste.
  • Reduce the use of fertilizer on lawns. Most established lawns do not need additional phosphorus to be healthy.
  • Do not dump lawn clippings, leaves or other yard waste into storm drains, creek beds, lakes or other waterways.
  • Have your septic system inspected and pumped at least every three to five years to help ensure it operates properly.
  • Use silt fences, containment barriers and other best management practices at residential and commercial construction sites to prevent runoff of nutrient-laden sediment.
  • Plant and maintain vegetative buffer strips along shorelines of lakes, ponds and streams. Native plants are much more effective at filtering runoff than the typical grass species found on residential lawns. See the Remarkable Riparian webpage for free digital lessons on riparian habitat function.
  • Learn more about water quality issues and steps you can take to improve water quality in your watershed. See the Texas Watershed Steward website for information on upcoming workshops and online resources such as training videos and the curriculum handbook.

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. There have been harmful algae blooms on Lady Bird Lake every year since then. We have also detected harmful algae on Lake Austin.

Current Status

Red bud isle in Austin, TX with harmful algae blooms. Green algae on the lake on Monday, March 4, 2024.

April 12, 2024: Storms have washed away a lot of the algae on our lakes, but there’s still some present along shorelines and around rocks. It is likely to return quickly as the weather warms. Be cautious! There may be toxic Cyanobacteria mixed in with other types of algae and vegetation. Please treat all algae like it may be toxic. See the recommendations farther down this page.

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:

You can find information on symptoms on the Centers for Disease Control and Prevention’s website, Illness and Symptoms: Cyanobacteria in Fresh Water. For more resources for physicians and veterinarians, please scroll down to the “Additional Resources” section of this page.

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).

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

Testing, Monitoring and Mitigation

To understand trends with harmful algae, we monitor three sites on Lake Austin and three sites on Lady Bird Lake, visiting them every other week throughout the summer. We also monitor one site on Lake Walter E. Long, visiting it at least three times during the summer and fall. Please note that the monitoring program provides a snapshot of conditions at specific locations at specific points in time, and is not suitable for determining the safety of an area for recreational use. Environmental conditions may change rapidly between testing dates and conditions may vary throughout the lake. Negative results in a single sample do not necessarily indicate that an area is free of harmful algae.

In 2023, we conducted a study of springs, which included sampling algae at Barton Springs Pool, Backdoor Spring on Barton Creek, Bluff Spring on Onion Creek, Harris Spring on a tributary to Onion Creek, Kizer Spring on Williamson Creek and Cold Spring on Lady Bird Lake.

We are treating specific areas of Lady Bird Lake to lower the nutrient levels in the lake. This may help reduce the amount of harmful algae. Learn more about Harmful Algae Mitigation.

Red dots indicate biweekly monitoring sites for harmful algae.

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
  • Microcystin
  • 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. As a veterinarian, I tell clients to never let their dog swim in a a stock pond or tank, culverts, stagnant water, and low flowing creek with warm water. If you live in Austin avoid RED BUD ISLE year round.

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.

Additional Information

Resources for physicians

Resources for veterinarians

Resources for the public

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