What’s Lurking in the Water – Understanding Blue-Green Algae

Weather and water conditions in many parts of the country have created or will create conditions favorable for the rapid growth of blue-green algae. Please be on alert with your horses, other animals and yourselves, and use precaution around water sources.

These single-celled organisms are actually algae-like bacteria instead of being true algae and are also referred to as Cyanobacteria.  They grow rapidly and may produce the pea-soup green color in some bodies of water, along with some foul odors.  The rapid growth periods, called “blooms” most frequently occur when there is a combination of warm weather, intermittent or limited rainfall and an accumulation of nutrients, particularly phosphorus and nitrogen. Blooms can range in color from green, to blue, brown or red. Water sources of fresh, brackish or salt water can all be affected by harmful algal blooms. Most often, slow moving water sources are the most suspect, although harmful algal blooms can occur in any water source with favorable conditions.

The planktonic groups produce the pea green water while the mat-forming groups produce dark mats that start on the bottom and float to the surface.  The planktonic species (Anabena, Aphanizomenon and Microcystis) are believed to be most likely to produce toxins which can be harmful or fatal to animals when ingested. Although, you cannot tell by looking at the bloom whether or not cyanotoxins exist. (Fact Sheet on Toxic Blue-Green Algae, Purdue University, Carole A. Lembi)

Toxins may be ingested when animals drink the water, when they lick their coats after being in the water, or when they inhale water droplets.  Animals are more likely to consume the water if fresh, clean water supplies are limited from other sources. Not all animals are deterred by foul odors that may be produced from the blooms.  Animals that drink or have exposure to the water during a period when cyanotoxins are being produced may be affected, but toxins are not always produced when there is a bloom.

Providing a source of fresh, clean, safe drinking water is the best way to avoid causing animals to consume questionable water.  If animals go swimming, they should be cleaned off before they have a chance to lick their coats, try not to engage in physical exertion near the water supply where inhaling water droplets could occur.

Preventing access to waterways is one way to prevent toxin exposure. Swimming in, contact with, breathing in water droplets or drinking water in ponds/lakes/streams is not recommended during temperatures or conditions that are favorable for blooms to exist. Most often slow moving water or calm water that has a greenish appearance are those most suspect to algal blooms, however they can exist an any water source if the conditions have been favorable. If contact has occurred watch for symptoms and promptly notify your veterinarian. When in doubt keep your animals and yourselves out of the water. Provide access to fresh, clean water at all times for your animals.

Toxic symptoms may include:

  • Diarrhea
  • Vomiting
  • Rash and skin irritation
  • Difficulty breathing
  • Seizure
  • Death

While not all “blooms” may produce toxins, avoiding exposure to or consumption of suspect water is recommended.  Risks of illness after the blooms are gone are low, however some toxins can still remain in the water once the blooms are gone. More information is available from local and state pollution control sites or extension sites. Health Departments recommend, when in doubt, keep out of the water.

Preventing run-off of nutrients into ponds and lakes is also important to help reduce the risk of these algae blooms.  Keeping vegetation around water sources can help naturally filter. Drought conditions in some areas have also increased the concentration of nutrients in the remaining water in ponds, lakes and streams.