Summer Brings Increased Risk of Toxic Cyanobacteria

Jul 02, 2025

By Miranda Meehan and Jake Galbreath

Cyanobacteria, also known as blue-green algae, can produce toxins that are harmful to livestock, wildlife and people. North Dakota State University Extension specialists have received reports of cyanobacteria blooms in livestock water sources. 

Miranda Meehan, NDSU Extension livestock environmental stewardship specialist, says the growth of this bacteria is facilitated by high temperatures.

“The hot, dry conditions projected for July are perfect for the production of cyanobacteria,” says Meehan.

Additionally, the North Dakota Department of Environmental Quality recently reported a cyanobacteria bloom on McDowell Dam. For a list of reported blooms, visit their website at https://deq.nd.gov/WQ/3_Watershed_Mgmt/8_HABS/Habs.aspx.

Cyanobacteria is caused by an excess of nutrients, particularly nitrogen and phosphorus. 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.

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. 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, according to Meehan.

Some species of cyanobacteria can be toxic when livestock and wildlife ingest them. Toxicity is dependent on the species consuming the water, the concentration of the toxin or toxins and the amount of water ingested.

Cyanobacteria can produce neurotoxins and liver toxins. Signs of neurotoxin poisoning can appear within five minutes to up to several hours after ingestion. In animals, symptoms include weakness, staggering, muscle tremors, difficulty in breathing, convulsions and, ultimately, death

Source : ndsu.edu
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