Toxic Algae in Lakes and Ponds Can Kill Your Dog

Before heading out to the pond with your dog for a swim, be sure to check the water for possible toxic algae first.

This algae was responsible for 4 dog deaths in 2011. By: Kansas City District
This algae was responsible for 4 dog deaths in 2011. By: Kansas City District

Taking your dog to the lake to play fetch is a common summer activity — but the quality of the water could mean disastrous results for your pet.

Two dogs recently became ill after playing fetch in Red Rock Lake in western Minnesota, and one of the dogs later died. The suspected culprit was blue-green algae, and officials are warning people to keep pets and children away from water with algae.

This is not the first time a dog has died from ingesting algae from a Minnesota lake. Last year, a dog named Copper died after ingesting algae from Prairie Lake.


Dangerous and sometimes deadly algae can show up not only in lakes but also in oceans, ponds, streams and lakes. Toxic algae can also bloom in outdoor water bowls, so always keep them clean.

As responsible pet caregivers, we should understand where this algae is found and how we can avoid it.

Summer heat often results in the overgrowth of algae. Although not all algae is bad, blue-green algae (cyanobacteria) can be harmful and sometimes fatal to dogs and humans.

What Is Toxic Algae?

Although the toxic algae is sometimes known as “red tide,” it is not always red and occurs in many colors such as blue, blue-green, yellow or brown. The toxic algae often emits a bad, smelly odor, but sometimes it’s odorless.

Because the smell is not consistent, you should not try to identify it by its smell. Cyanobacteria algae occurs in cloudy patches of algae. These blooms look like foam or scum floating on the surface of water. It can occur in patches or appear to cover the entire surface of the pond.

When Is It a Concern?

The toxic algae blooms typically appear in late summer and early fall in the Northeast, but they can appear at any time in warmer climates. Heat is what causes the overgrowth of algae, so locations with warmer climates year round are more susceptible to cyanobacteria in the water.

Where It Grows

Unfortunately, the toxic bacteria is not limited to one area. It has been documented all over the world. Toxic algae can occur in any body of water but is especially common in freshwater ponds — a popular location to take your dog for a swim. Salty/brackish water is also known to harbor this bacterium.


The video below shows a man on Lake Erie navigating through toxic algae:

Signs of Exposure

If you are swimming with your dog and notice that he is experiencing any of these symptoms, contact a veterinarian immediately:

Other Dangers

Other than the concern of cyanobacteria, there are other bacteria lurking in natural ponds.

Because natural ponds are visited by wildlife whose urine and feces host a number of illnesses, contagious bacteria and diseases, ponds are breeding grounds for concerning bacteria. When your dog drinks that pond water, he is at risk for contamination.

Some of the common bacteria found in natural ponds are:

  • Giardia: A common bacterium found in contaminated feces, once ingested it can cause lasting diarrhea. If you suspect your dog has giardia, have your vet test the dog’s stool.
  • Coccidia: This is transmitted from dog to dog through feces. It can lie dormant in the dog’s body undetected but causes lasting diarrhea. It can also be found by fecal test done by your vet.
  • Leptospirosis: Natural water contaminated with infected wildlife urine can cause severe illness in dogs when ingested. A vaccine is available to protect your dog against lepto contamination.

Despite the handful of concerns surrounding natural pond water and allowing your dog to take a dip, we’re not suggesting that you not let your dog swim. Part of being a responsible pet caregiver is understanding the risks involved in your decisions.

If you suspect your dog has been contaminated, contact your vet for instructions on how to ensure your dog’s health and safety.


This pet health content was reviewed for accuracy by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed and updated Dec. 17, 2018.


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