As temperatures rise, so should agricultural producers’ caution around toxins on their operations.

Cyanobacteria, also known as blue-green algae, can produce toxins that are harmful to livestock, wildlife and people. North Dakota State University Extension specialists advise people to be on the lookout for cyanobacteria blooms in water sources.

Miranda Meehan, NDSU Extension livestock environmental stewardship specialist, says cyanobacteria growth is highly accelerated by warm to hot temperatures.

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

The North Dakota Department of Environmental Quality maintains a list of cyanobacteria blooms on lakes and reservoirs. For a list of reported blooms, visit  https://deq.nd.gov/WQ/3_Watershed_Mgmt/8_HABS/Habs.aspx.

The growth of cyanobacteria is driven by excess nutrients, particularly nitrogen and phosphorus. Manure and commercial fertilizers are often spread to enhance forage and crop production. When these products are misused, either through inappropriate application rates or timing, the potential for nutrient loss into surface water increases. When these nutrients enter surface water, they stimulate the 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 and just below the water surface. Live cyanobacterial blooms are commonly green but can also be red or yellow, and they often turn blue after the bloom dies and dries on the surface or shoreline, according to Meehan.

Some cyanobacteria species can be toxic when livestock and wildlife ingest them. Toxicity depends on the species consuming the water, the concentration of the toxin(s) 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 breathing, convulsions and, ultimately, death. Animals affected by liver toxins may exhibit weakness, pale-colored mucous membranes, mental derangement and bloody diarrhea, and they too may ultimately die.

Typically, livestock are found dead before producers observe symptoms. If cyanobacterial poisoning is suspected as the cause of death, producers should check the edges of ponds for dead wildlife.

Dr. Jake Galbreath, NDSU Extension veterinarian and livestock stewardship specialist, advises any rancher who suspects cyanobacteria poisoning as the cause of a livestock death should contact a veterinarian to conduct a necropsy.

“A veterinarian can determine which samples would be appropriate for each situation,” says Dr. Galbreath.

When collecting a water sample, follow NDSU Extension’s livestock water testing guidelines at ndsu.ag/watertesting-26.

Be sure to wear gloves, as cyanobacteria can be toxic to humans. Collect a sample of the suspected cyanobacterial bloom from the surface and deeper in the water. The sample should be kept cool, not frozen, and submitted 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 cyanotoxins.

For more information on sample collection and submission, contact a local NDSU Extension agent.

Laxmi Prasad, NDSU Extension water engineer, provides ways farmers and ranchers can prevent cyanobacterial poisoning of livestock:

• Reduce nutrient levels entering the water source by implementing a nutrient management plan or establishing buffer strips with perennial plant species.
• Create a designated drinking area where the risk of cyanobacteria is minimal.
• Fence off the pond and pump water from the pond to the water tank.
• Use water from other sources following periods of hot, dry weather.
• Pump water from the center of the water body well below the surface, where the bacteria are unlikely to concentrate, to a water tank.

“Unless steps are taken to reduce the nutrient load and minimize the potential for nutrients to enter the water body, the risk for cyanobacterial blooms will continue,” says Prasad.

Prasad also provides some management practices to consider to reduce nutrient loads:

• Properly apply nitrogen and phosphorus to fields — rate, time and amount and type of nutrients applied need to be considered.
• Adapt soil conservation practices that reduce erosion.
• Install hay or graze buffer strips to reduce the release of phosphorus as plants decompose.

Contact your local NDSU Extension agent for more information on cyanobacteria and nutrient management. Additional information regarding water quality can be found at ndsu.ag/water-quality-26.

NDSU Agriculture Communication – June 29, 2026

Source: Miranda Meehan, 701-219-9251, miranda.meehan@ndsu.edu

Source: Jake Galbreath, 701-231-5738, j.galbreath@ndsu.edu

Source: Laxmi Prasad, 701-231-4190, laxmi.prasad@ndsu.edu

Editor: Dominic Erickson, 701-231-5546, dominic.erickson@ndsu.edu