Understanding the Health Risks Posed by Algal Blooms

UT Health Austin neurologist explains how toxins from algae in waterways can be harmful to 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 August 25, 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 be mindful of protecting their actual dogs and other family, friends, and pets from algae in these bodies of water.

On August 17, 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. The Lady Bird Lake samples were collected at Red Bud Isle, Vic Mathias Shores, and Festival Boat Ramp while the Lake Austin sample was taken from Jessica Hollis Park. Additionally, toxins were detected at spring study sites at Barton Springs Pool, Backdoor Spring on Barton Creek, Bluff Spring on Onion Creek and Harris Spring on a tributary to Onion Creek, Kizer Spring on Williamson Creek, and Cold Spring on Lady Bird Lake.

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<br>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 board-certified neurologist David Paydarfar, MD, who serves as Director of UT Health Austin’s Mulva Clinic for the Neurosciences and is a part of UT Health Austin’s Pharyngeal High-Resolution Manometry care team.

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,” shares Dr. Paydarfar. “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 found in Lady Bird Lake was linked to the death of several dogs.

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), and digestive system (gastro-intestinal inflammatory toxins) as well as multiple organ systems at once (general cytotoxins).

Cylindrospermopsin, one of the cyanotoxins found in algae samples this summer, is known to affect multiple organ systems by preventing cells from making new proteins. Ingesting excessive levels of cylindrospermopsin or microcystin, another cyanotoxin identified in the city’s algae samples, is linked to liver and kidney damage.

Several of the cyanotoxins detected by the Watershed Protection Department, such as saxitoxin, are neurotoxins. Three of these toxins, dihydroanatoxin, homoanatoxin, and anatoxin, 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).

Under 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,” explains Dr. Paydarfar, “but symptoms have included fasciculations, paralysis, cognitive effects, such as delirium and hallucinations, and respiratory failure due to impaired respiratory muscle functioning.”

Warning Signs of Anatoxin Poisoning in Pets

“When it comes to symptoms of anatoxin poisoning in pets, symptoms may manifest very suddenly and require immediate attention,” warns Dr. Paydarfar. “It’s a relatively small molecule, so it gets into the system quickly.”

Early signs of anatoxin poisoning in pets that would warrant emergency evaluation include:

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

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

Then, you should call 3-1-1 to report the incident. “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,” says Brent Bellinger, a Watershed Department environmental scientist.

Keeping You and Your Pet Safe

You can help prevent algae ingestion by rinsing and toweling your dog off after swimming.

Keep yourself and your pet safe by staying 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,” shares Bellinger. “In those stagnant waters, you could have other bacteria, amoebas, viruses, or fungus.”

What Austinites Should Know

<Br>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

On June 5, 2023, the Watershed Protection Department initiated this year’s algae mitigation efforts by treating the Red Bud Isle area with lanthanum-modified bentonite, which traps phosphorus that would otherwise be used as a nutrient source for algae. More treatments are scheduled at other sites in the city’s recreational waters.

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.