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Be Aware of Toxic Cyanobacteria

Cyanobacteria, also known as blue-green algae, can produce toxins that are harmful to livestock, wildlife and people.

“The growth of this bacteria is facilitated by high temperatures,” says Miranda Meehan, North Dakota State University Extension livestock environmental stewardship specialist. “The hot, dry conditions we experience in the summer months are perfect for the production of cyanobacteria.”

“Cyanobacteria is caused by an excess of nutrients, particularly nitrogen and phosphorous,” says Mary Keena, NDSU Extension livestock environmental management specialist. “Manure and commercial fertilizers are spread to enhance forage and crop production. When these products are misused, either by inappropriate rate or timing of application, the potential for nutrient leaching to surface water is increased. When these nutrients enter surface water, they stimulate growth of cyanobacteria and other microorganisms.”

“There may be an increased potential for cyanobacteria blooms in some areas of the state this year,” says Meehan. “In 2021, nutrients applied to fields were not effectively mobilized and used by plants due to drought conditions. Widespread overland flooding in the spring of 2022 may have transported these nutrients to waterbodies, increasing nutrient loads and the potential for blooms.”

Given the current conditions, farmers and ranchers, and the public should be on the lookout for cyanobacteria blooms.

“Blue-green algae often occurs in stagnant ponds or dugouts with elevated nutrient levels, forming large colonies that appear as scum on or just below the water surface,” says Keena. “Live cyanobacterial blooms can be green, but also red or yellow, and often turn blue after the bloom dies and dries on the surface or shoreline.”

“Some species of cyanobacteria can be toxic when livestock and wildlife ingest them” says Dr. Gerald Stokka, NDSU Extension veterinarian and livestock stewardship specialist. “Toxicity is dependent on the species consuming the water, the concentration of the toxin or toxins and the amount of water ingested.”

Dr. Stokka added that cyanobacteria can produce neuro and liver toxins. Signs of neurotoxin poisoning can appear within five minutes or up to several hours after ingestion. In animals, symptoms include weakness, staggering, muscle tremors, difficulty in breathing, convulsions and death.

“Animals affected by liver toxins may exhibit weakness, pale-colored mucous membranes, mental derangement, bloody diarrhea and, ultimately, death,” says Stokka. “Typically, livestock are found dead before farmers and ranchers observe symptoms. If cyanobacterial poisoning is suspected as the cause of death, check the edges of ponds for dead wildlife.”

Farmers/ranchers who suspect cyanobacteria poisoning as the cause of a livestock death, should contact a veterinarian to conduct a necropsy. Contact your veterinarian to determine which samples would be appropriate for your situation.

When collecting a water sample, follow NDSU Extension’s Livestock Water Testing Guidelines ( Contact your local Extension agent for a sampling container or assistance collecting samples.

“Be sure to wear gloves, as cyanobacteria can be toxic to humans,” says Meehan. “Collect a sample of the suspected cyanobacterial bloom from the surface of the water and deeper in the water. The sample should be kept cool but not frozen, and submitted it to the NDSU Veterinary Diagnostic Laboratory or a commercial laboratory.”

The sample can be evaluated microscopically for algae, or the water can be analyzed for several of the toxins at commercial labs at a higher cost.

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