ODH warns about toxic algae in Ohio waters

Photo courtesy of Ohio EPA
Photo courtesy of Ohio EPA

Within the past month, there have been multiple reports of Harmful Algal Blooms (HABs) in bodies of water across Ohio. In response, the Ohio Department of Health (ODH) wishes to share the following information with Ohio veterinarians.

Photo courtesy of Ohio EPA
Photo courtesy of Ohio EPA
Photo courtesy of Ohio EPA
Photo courtesy of Ohio EPA

Proliferation of some blue-green algae (cyanobacteria) can produce toxins that can cause illness and death in both humans and animals. Cyanobacterial blooms form in warm, slow-moving waters that are rich in nutrients such as fertilizer runoff or septic tank overflows.

Blooms, which can look like colorful foam, scum or mats on water, most often occur when the water temperature rises. Blooms can occur in marine, estuarine and fresh waters, but the blooms of greatest concern are those that occur in fresh water, such as reservoirs or recreational waters. The algae can produce multiple toxins and they are primarily classified as either neurotoxins or hepatotoxins.


An exposure to an algal bloom includes having had known contact with or ingesting HAB-contaminated water or scum or having eaten any dead animal near a body of water with an algal bloom. Animals are at an increased risk for severe illness because they are not hesitant about swimming in or ingesting HAB-contaminated water. Further exposure can occur when animals lick their fur after swimming or by eating the surface scum on the beach.

Clinical signs

Onset of illness to these toxins is rapid, from minutes to hours with anatoxin or saxitoxin (neurotoxins), and from hours to days with hepatotoxins such as microcystin.

In animals such as cattle, sheep, horses, pigs and dogs, there may be clinical signs and clinicopathologic data suggestive of liver failure if algal poisoning is caused by microcystin. In such cases, the liver may be enlarged or contain areas of hemorrhage, accompanied by hepatocellular necrosis. Other algal toxins, such as anatoxins, may result in no gross or microscopic morphologic lesions.

Clinical signs of acute toxicity include:

  • vomiting
  • weakness
  • paralysis
  • rash
  • seizures
  • sudden death


Currently, there are no commercially available tests for toxins. The Ohio Department of Agriculture Animal Disease Diagnostic Lab (ODA-ADDL) can perform histopathology on sections of formalin-fixed liver, kidney and brain tissue to support a diagnosis. Tissues from suspect cases can be sent for further analysis to reference labs that offer this testing. The ADDL Veterinary Pathologists and Toxicologist would provide final diagnosis. Contact ODA-ADDL at 614.728.6220 for consultation prior to submission of necropsy cases for specifics.


Animals often serve as sentinels for human illness; therefore, we encourage veterinarians with knowledge of an animal case or suspected case of HAB exposure and illness to report this to the local health department where the animal resides using the animal illness report. This information may be helpful in identifying harmful algal blooms so the public can take steps to prevent exposure to themselves and other animals.

Unusual mortality and morbidity in wildlife should be reported to the county wildlife officer or to the Ohio Department of Natural Resources at 800.945.3543.

For More Information


Disease in Animals

Human illness


—Submitted by Joanne Midla, VMD, MPH
Public Health Veterinarian, Ohio Department of Health

Download a printable version of this notice from ODH

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