What are blue-green algae and can they hurt my family and pets?

Blue-green algae are a group of naturally occurring bacteria found in both fresh and salt water.

green colored water near a boat ramp
Algal blooms occur more frequently with warmer temperatures and excess nutrients. | Photo Credit: Paul Terrio, U.S. Geological Survey

When temperatures soar in the summer months, many people and their pets, love to take to the water to help beat the heat. While swimming is usually a perfectly safe summertime tradition, there are some emerging threats that water enthusiasts and pet owners should be aware of.

Each summer, news stories break throughout the country about dogs dying after swimming in water. The usual culprit:  cyanobacteria, commonly known as blue-green algae.

Blue-green algae are a group of naturally occurring bacteria found in both fresh and salt water. The hardy bacteria can also be found on just about every type of habitat—damp soil or even briefly moistened bare rock can harbor the bacteria. Although a blue-green color is most common, the bacteria can also be red, brown, or even purple. 

In late summer and early fall, when the water temperatures have warmed to their highest point of the year, conditions are often favorable for excessive growth of cyanobacteria, also known as a blue-green algal bloom.  In addition to warm temperatures, blue-green algal blooms are fueled by an overabundance of nutrients, particularly phosphorus and nitrogen. Excess phosphorus and nitrogen can enter bodies of water through many sources, including fertilizer runoff and untreated sewage from manure spreading, leaking septic systems, or wastewater overflows. 

People typically recognize blue-green algal blooms by the appearance of a scum on the water’s surface, and/or bluish-green stained water, many times accompanied by a foul odor. However, blue-green algal blooms can also occur in water that appears clear. Blue-green algal blooms are likely to be more prevalent in lakes and ponds, where the water is less prone to being mixed up and dispersed from wind and waves.

The presence of blue-green algae in a water body is not abnormal. However, it can become a concern because in some instances, blue-green algae can produce harmful toxins. Toxins released from blue-green algae can be harmful to both humans and pets, potentially damaging the brain, liver, and kidneys of an animal. According to the Centers for Disease Control and Prevention (CDC), exposure to cyanobacteria can occur through ingestion, inhalation, or skin contact. This means that being in or around an algal bloom can expose a person or pet to the toxins in a variety of manners. Signs and symptoms of exposure can include gastrointestinal ailments, sore throat or respiratory problems, or irritation in the eyes or on the skin.

There are several important measures that can be taken to minimize you or your pet’s exposure to harmful cyanobacteria. The CDC recommends avoiding drinking or recreating in water that is discolored, has a bad odor, or has visible scum or foam on the surface. Pets that inadvertently enter suspect water should be rinsed off as quickly as possible and monitored closely for signs of sickness or distress. Bringing along fresh drinking water for your pet is also a good idea, regardless of whether any signs of suspect water are present.

Also, it’s important to note that just because water has a certain coloration or substances floating on it does not mean it is harboring harmful cyanobacteria. There are many other naturally occurring and human-caused phenomena that can be mistaken for harmful algal blooms. For additional information, Michigan State University Extension natural resources educators can provide educational programming and assistance with invasive organisms and invasive aquatic plants. 

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