Toxic Algae Signs and Safety Tips
AgriLife Extension expert shares tips to prevent cyanobacteria bloom exposure as temperatures rise.
May 6, 2025
![Harmful cyanobacteria blooms can appear in many colors, including green, blue, red and more. While the appearance of a bloom can be varied, a tell-tale sign is the presence of dead aquatic life. [Brittany Chesser/Texas A&M AgriLife.]](https://cd.angus.org/-/jssmedia/project/american-angus-association/angus/angus-media/angus-beef-bulletin/abbx-articles/2025/04/0525extrahn_toxicalgae-16x9.jpg?mw=1440&iar=0)
Harmful cyanobacteria blooms can appear in many colors, including green, blue, red and more. While the appearance of a bloom can be varied, a telltale sign is the presence of dead aquatic life. [Brittany Chesser/Texas A&M AgriLife.]
by Sarah Fuller, Texas AgriLife Extension
Whether treading water in a river or diving into a reservoir, summer fun should come with a little caution. As temperatures climb, so does the risk of potentially harmful cyanobacteria blooms — commonly known as blue-green algae — that can pose serious health risks to people, pets and livestock.
Warming water temperatures create the perfect environment for these toxic, photosynthetic bacteria, says Brittany Chesser, Texas A&M AgriLife Extension Service aquatic vegetation management program specialist and lead diagnostic scientist at AgriLife Extension’s Aquatic Diagnostics Laboratory, Bryan-College Station.“Cyanobacteria are some of the oldest organisms on earth and are found widely throughout the environment — from freshwater and marine environments to the soil,” Chesser says. “But toxicity becomes a concern when environmental conditions trigger large-scale population growth and they begin releasing toxins to compete for nutrients and other resources.”
Chesser shares information about the organisms, their environmental triggers, and potential signs of a harmful bloom.
Cyanobacteria blooms come in many shapes and colors
Awareness is important, Chesser says. “The most important thing you can do is to educate yourself on possible visual cues, and, if you are a pond owner, be aware of nutrient levels that can facilitate a bloom.”
Not all cyanobacteria produce toxins, and not all blooms are visible. Depending on the species, blooms can form surface scum or clumps that resemble wool or cotton. Others can look like an accumulation of grass clippings.
“The blooms can appear in many colors, including green, blue, purple, red or no color at all,” Chesser says. “Generally, the blooms are vibrant and look like spilled paint that has collected in a downwind area of a waterbody.”
Cyanobacteria can regulate their buoyancy in the water column to take advantage of ideal nutrient and light conditions, so they may gather several inches below the water’s surface, Chesser says.
She says one telltale sign of a possible bloom is dead aquatic life such as fish, turtles or frogs.
What causes toxic algae blooms?
Algal blooms thrive in warm, slow-moving water rich in nutrients, especially phosphorus.
“During periods of drought when water levels drop and become stagnant, we see the organisms and nutrients concentrating, creating conditions conducive to a bloom,” Chesser says.
Rain events can also facilitate blooms by washing large amounts of nutrients from the surrounding landscape into the water body.
“Especially with ponds, it is important to continually incorporate nutrient mitigation strategies early and often,” she says. “Don’t dispose of grass clippings in your pond, reduce the amount of leaf litter in your pond, and don’t fertilize the turf or pasture immediately surrounding the area.”
Signs of cyanobacteria exposure in people and pets
Symptoms of cyanobacteria toxicity vary depending on the species encountered and how you are exposed.
Chesser says while some cyanotoxins can cause symptoms similar to irritation or an allergic reaction, others, known as hepatotoxins, bioaccumulate and can damage the liver. The most acute toxins produced are neurotoxins, which affect the central nervous system.
“This neurotoxin exposure is typically associated with the death of companion animals,” Chesser says. “In a very short time after leaving the water, an animal can begin exhibiting symptoms, such as disorientation, that progress rapidly.”
Chesser says if you suspect you or your pet has been exposed to a cyanobacteria bloom, seek medical or veterinary care as soon as possible.
Testing is available, but is not foolproof
AgriLife Extension offers a base detection test for the presence of cyanobacteria hepatotoxins. However, the test does not measure total toxin levels or detect every possible toxin produced by cyanobacteria.
“If you are concerned your pond may hold the potential for a harmful bloom, you can test your water’s total nutrients to paint a better picture of whether the conditions are right for a cyanobacteria bloom,” she says. “This can allow you to take proactive measures such as adding nutrient binders or additives to reduce those excess nutrients.”
Editor’s note: Sarah Fuller is natural resources communication strategy leader for Texas A&M AgriLife Extension.
Angus Beef Bulletin EXTRA, Vol. 17, No. 5-A
Topics: Health , Human Health
Publication: Angus Beef Bulletin
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