Understanding the Health Risks Posed by Algal Blooms

A UT Health Austin neurologist explains how toxins from algae, such as those found in Lady Bird Lake and Lake Austin this summer, can harm you and your pets

Reviewed by: David Paydarfar, MD
Written by: Lauren Schneider

A blue heeler mix dog is standing on a paddle board with its owner on Lady Bird Lake.

Update: This piece was edited on May 24, 2023 to reflect the most recent information from the Watershed Protection Department.

While Barton Springs, Lake Austin, and Lady Bird Lake provide much-needed recreational opportunities during the dog days of summer, Austinites should protect their actual dogs from algae in these bodies of water.

On May 15, 2023, the City of Austin Watershed Protection Department announced that blue-green algae was detected at all the department’s monitoring sites in Lady Bird Lake and Lake Austin other than Walsh Boat Landing. While no information about the toxin content of this algae is available yet, the department advises Austinites to proceed as though all algae is toxic.

Harmful Algal Blooms on the Rise

Blue-green algae, also known as cyanobacteria, produce several classes of toxic compounds collectively known as cyanotoxins. “These cyanobacteria are amazing factories of small molecules,” says neurologist David Paydarfar, MD, Director of the Mulva Clinic for the Neurosciences at UT Health Austin.

According to Dr. Paydarfar, a combination of factors induces cyanotoxin production in blue-green algae, particularly during the summer. “The heat, sunlight, and agricultural runoff lead to this major amplification in production.” These sharp increases in cyanobacteria levels and cyanotoxin production are known as harmful algal blooms, and they pose health risks to humans and animals who are exposed to the toxins, typically by ingestion.

Harmful algal blooms have been on the rise in Austin in the past few years. The city first took notice in 2019 when a harmful bloom of algae containing dihydroanatoxin in Lady Bird Lake was linked to the death of several dogs; the toxin has been detected in the lake every year since, including this year at Red Bud Isle.

The specific health risks associated with these algal blooms depend on which cyanotoxins are produced. Cyanobacteria can produce toxins that affect the nervous system (neurotoxins), liver (hepatotoxins), skin (dermal toxins), digestive system (gastro-intestinal inflammatory toxins), or multiple organ systems at once (general cytotoxins). For example, cylindrospermopsin, a cyanotoxin identified in 2021 at Sculpture Falls after reports of illness, is known to affect multiple organ systems by preventing cells from making new proteins. The City of Austin prohibited swimming at the site until toxin levels subsided later in the season.

Dihydroanatoxin-A and homoanatoxin-a, the two toxins found in algae samples this summer, belong to a family of neurotoxins known as anatoxins. Anatoxins act on both the central nervous system (the brain and spinal cord) and peripheral nervous system (all other nerves) by binding to receptors on cells called nicotinic acetylcholine receptors (nAChRs).

In normal conditions, a chemical produced by neurons called acetylcholine binds temporarily to these receptors, facilitating certain types of cellular communication. Anatoxins bind nAChRs “almost irreversibly,” says Dr. Paydarfar. “It just wreaks havoc.”

In addition to binding neuronal receptors, anatoxins bind to nAChRs on muscle cells, disrupting the process by which the nervous system gives instructions to muscles. This initially causes muscle contraction and fasciculations, tiny contractions of only the muscle fibers controlled by a single motor neuron. Because the toxin never leaves the receptor, affected muscle cells reach a point where they can no longer be activated, resulting in paralysis.

Few cases of anatoxin poisoning have been reported in humans, but Dr. Paydarfar notes that symptoms have included fasciculations, paralysis, cognitive effects like delirium and hallucinations, and respiratory failure due to impaired respiratory muscle functioning.

Warning Signs of Anatoxin Poisoning in Pets

According to Dr. Paydarfar, early signs of anatoxin poisoning in pets that would warrant emergency evaluation include:

  • Confusion
  • Behavior change
  • Ataxia (not walking straight) or imbalance
  • Convulsions

Symptoms of anatoxin poisoning may manifest very suddenly and require immediate attention. “It’s a relatively small molecule, so it gets into the system quickly,” says Dr. Paydarfar.

Keeping You and Your Pet Safe

Because anatoxin and its derivatives are so fast-acting, you should call a veterinarian right away if your pet shows signs of ingestion.

The next step is to call 3-1-1 to report the incident, according to Watershed Department environmental scientist Brent Bellinger. “They have questionnaires to determine if it was a pet illness and if a human possibly was exposed, at which point it’ll be routed to myself and/or Austin Public Health for follow-up.”

Bellinger adds you can prevent algae ingestion by rinsing and toweling your dog off after swimming and keeping yourself and your pet out of water with the following characteristics:

  • Scum or mats floating on the surface
  • Stagnant
  • Odd smell
  • Discolored

“It might not even be a toxin issue. In those stagnant waters, you could have other bacteria, amoebas, viruses, or fungus,” Bellinger says.

What Austinites Should Kow

No Cyanotoxins Detected in Drinking Water Supply

The Austin Water website states that “current tests are non-detect for cyanotoxins in raw or treated drinking water.” The department routinely tests both raw water from Lake Austin and Travis as well as water from the Handcox, Davis, and Ullrich Treatment Plants. In 2021, Austin Water acquired new equipment to allow in-house testing for cyanobacteria and cyanotoxins in drinking water samples.

Controlling the Spread in Recreational Waters

The Watershed Protection Department is currently developing its 2023 plan to treat local waterways with Phoslock, a gritty clay substance named for its ability to “lock” away phosphorus which the algae otherwise would use as a source of nutrition.

The department also collects algae samples every two weeks from three locations on Lake Austin and another three sites on Lady Bird Lake. Data about the toxin content of these samples will become available in June.

Headed outside this summer? View these sun safety tips.

For more information about the Mulva Clinic for the Neurosciences or to schedule an appointment, click here or call 1-833-UT-CARES (1-833-882-2737).

About UT Health Austin

UT Health Austin is the clinical practice of the Dell Medical School at The University of Texas at Austin. We collaborate with our colleagues at the Dell Medical School and The University of Texas at Austin to utilize the latest research, diagnostic, and treatment techniques, allowing us to provide patients with an unparalleled quality of care. Our experienced healthcare professionals deliver personalized, whole-person care of uncompromising quality and treat each patient as an individual with unique circumstances, priorities, and beliefs. Working directly with you, your care team creates an individualized care plan to help you reach the goals that matter most to you — in the care room and beyond. For more information, call us at 1-833-UT-CARES or request an appointment here.