Protecting Your Herd: Managing Harmful Algal Blooms (HABs) 

HEATHER NIX
Upstate Water Resource Agent

CHRISTOPHER LeMASTER
Area Livestock & Forage Agent

As we move into the warmer months, ensuring cattle have access to fresh, clean water is a primary management concern. Many producers rely on surface water sources; however, this practice introduces risks, most notably Harmful Algal Blooms (HABs), which can have rapid and fatal consequences for livestock. 

What are Harmful Algal Blooms (HABs)? 

 HABs include rapid overgrowths of cyanobacteria (formerly called blue-green algae) in water bodies. Unlike true algae, cyanobacteria can produce toxins that are harmful to humans, pets, and livestock. These blooms may appear as a “spilled paint” scum, pea soup, grass clippings, or thick mats on the water surface and can vary in color from blue to bright green to brownish-red. 

Effects on Cattle 

Cyanobacteria can produce over 1,000 types of poisonous compounds, known as cyanotoxins, which are released when the cells die and rupture. Cyanotoxins can attack the skin, liver, cells, or nervous system and can produce symptoms within minutes, days, or months following exposure. Health impacts depend on specific cyanotoxin(s), concentration, route of exposure (ingestion, contact, etc.), and length of exposure. Symptoms can vary widely, in livestock watch for skin rash or increased sensitivity to sun exposure, diarrhea, weakness, respiratory distress, muscle tremors, premature births, or fetal death.  

Prime Conditions for HAB Growth 

Cyanobacteria thrive when environmental conditions provide a “perfect storm” for growth: 

• Stagnant Water: Still or low-flow water, such as farm ponds or backwater areas. 

• Nutrient Rich: High levels of phosphorus and nitrogen, possibly from fertilizer runoff or direct manure input. 

• Warm Temperatures: Prolonged sunlight and warm water temperatures (above 77ºF) during warm weather. 

How to Monitor for HABs 

In 2025, the South Carolina Department of Environmental Services (SCDES) issued its first Recreational Watch after identifying toxin-producing HAB species in Lake Hartwell on April 30th, with the latest Recreational Advisory issued for Lake Thurmond on November 25th. Because of this wide window, producers should regularly inspect ponds and other water sources, especially on the downwind pond edges where wind and waves concentrate the blooms. 

• The Stick Test: If you can lift the algae out of the water with a stick, it is likely non-toxic filamentous algae. If it breaks apart and cannot be lifted or coats the stick like paint, it may be cyanobacteria. 

• The Jar Test: Place a water sample in a clear jar and refrigerate it overnight. If the algae floats to the surface, it is a strong indicator of cyanobacteria. 

• Submit a Sample: A Clemson University lab can confirm identification and provide management recommendations for $20 (in-state); samples can be dropped off at any county Extension office. Results typically take 7-10 business days. See Submitting an Algae Sample for Identification (https://hgic.clemson.edu/factsheet/submitting-an-algae-sample-for-identification/) for more information.  

Action Steps: Response and Recovery 

If you suspect a bloom is present, take immediate action to protect your herd: 

1. Remove Animals (and People): Immediately exclude livestock from the suspected water source using temporary fencing or by moving the herd to a different pasture. 

2. Provide Alternative Water: Ensure animals have access to a clean, reliable supply, such as well water or a municipal source. Note: Be aware that even “clean” sources can become contaminated if equipment (troughs, hoses, or buckets) has been exposed to the bloom. Be sure water (in troughs) is regularly refreshed and thoroughly clean and flush any shared infrastructure. 

3. Report to the Clemson HAB Response Team: Contact your local Livestock or Water Resource Agent immediately. Our statewide response team can assist with rapid sampling and positive identification to determine if the bloom is toxic. Having pictures of the pond (or water source) and a water sample (including potential HAB growth) may be helpful. 

References 

• Do It Yourself: Visual Indicators, Stick Test, and Jar Test for Cyanobacteria. (2022). Nix HB, Hains J, Sahoo D, & White SA. HGIC 1899. Home & Garden Information Center by Clemson Extension. https://hgic.clemson.edu/factsheet/do-it-yourself-visual-indicators-stick-test-and-jar-test-for-cyanobacteria/ 

• Harmful Algal Blooms: Prevention, Response, and Avoidance Manual (2023). Nix, H., Sahoo, D., White, S. A., Hains, J., & Busari, I. Clemson Cooperative Extension. https://dc.statelibrary.sc.gov/entities/publication/1daac8c5-90c7-4c58-a1f4-7189188c085a 

• Livestock Ponds in South Carolina. (2023). Davis RH, Nix HB, White SA, & Smith WB. LGP1156. Clemson University Land-Grant Press. https://lgpress.clemson.edu/publication/livestock-ponds-in-south-carolina/  

• Livestock Water Quality. Clemson University Land-Grant Press. 

• Submitting an Algae Sample for Identification. (2025). Nix HB, Hains J, Williamson M, & Low D. HGIC 1889. Home & Garden Information Center by Clemson Extension. https://hgic.clemson.edu/factsheet/submitting-an-algae-sample-for-identification/ 

Photo Credit: Emily Bores, SCDES