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Dog drinking pond water with algae

The essentials

  • It’s not actually algae — Blue-green algae is a blanket term for cyanobacteria. Actual algae is either a plant or protist, which is a one-celled organism that lives by itself or in groups. Algae is usually benign. Blue-green algae, on the other hand, is a cyanobacteria that produces toxins when it blooms in large numbers.
  • Stagnant water during hot weather poses the largest risk — Beware of harmful algal blooms (HABS) in standing fresh water such as ponds and lakes during the middle of the summer when water temperatures rise.
  • Blue-green algae is also found in the ocean — Although most harmful cyanobacteria are found in stagnant freshwater, it can also grow in the ocean. Be sure to pay attention to warnings from local health departments before you take your dog to the beach.

Cyanobacteria grow in lakes, ponds, rivers, and oceans. As primary sources of oxygen in aquatic environments and among the oldest organisms on earth, cyanobacteria aren’t always bad. In fact, given their potential to cure lung cancer and possibly serve as a source of fuel in the future, cyanobacteria often have an important role to play.

However, when their population surges, a subgroup of cyanobacteria creates harmful algal blooms (HABS) . These blooms release microcystins, toxins that can cause vomiting, diarrhea, seizures, serious liver or neurological damage, and even death in humans and pets. Let’s talk more about what cyanobacteria are, and how we can protect our pets during the summer when they’re most likely to take a swim.

Biological classification of blue-green algae

Although they’re most commonly referred to as blue-green algae, cyanobacteria aren’t technically algae, scientifically speaking. Algae is a eukaryotic organism that either belongs to kingdom protista or kingdom monera depending on the species. Eukaryotic organisms have a defined nucleus.


Kingdom and phylum of blue-green algae

Belonging to the kingdom Bacteria under the phylum Cyanobacteria, what we call “blue-green algae” is a prokaryotic organism. As such, it is a single-celled organism without a defined nucleus. Don’t confuse prokaryotic with protist, which is a single-celled organism with a nucleus, like some types of true algae. Cyanobacteria were once classified as algae, but they were removed once it was discovered that they don’t have a nucleus.

Divisions and subdivisions

There is a little bit of a gray area when it comes to scientifically classifying what we commonly pronounce to be algae and bacteria. What we typically call “blue-green algae” is actually cyanobacteria that usually affects freshwater, but can also impact the ocean.

In a similar way, the red tide phenomenon that mostly affects marine life is also an algal bloom, but the culprit isn’t related to cyanobacteria. Nonetheless, this type of algal bloom is toxic to both dogs and humans. The species Kerenia brevis that frequently causes red tides belongs to the kingdom Chomesta under phylum Myzozoa, and yet it is also considered algae.

Where does blue-green algae live? 

Just as toxins from the red tide most commonly affect oceans, microcystins from cyanobacteria most frequently plague freshwater areas—especially stagnant water in hot temperatures. Pollution and fertilizer that drain off into freshwater areas catalyze the growth of these toxins. Microcystins themselves are invisible to the naked eye, but you can sometimes see the algal blooms on the surface of the water. It usually looks like someone dumped a can of bright green paint into the water.

Other types of algae have this appearance, so it doesn’t always mean there are harmful cyanobacteria in the water. However, if you see algal blooms, it’s best not to get in the water to be safe.

The life cycle and reproduction of blue-green algae

Cyanobacteria reproduce asexually through cellular fission. Hot weather, stagnant conditions, fertilizer drain off, septic tank drainage, and other pollution accelerate their growth. When the cyanobacteria population booms, algal blooms result and the water appears to be covered with a layer of lime green slime.

Unfortunately, there’s no way to completely eradicate blue-green algae. You can use chemicals like chlorine in certain environments, such as backyard swimming pools, but such chemicals wouldn’t be safe to use in nature because they would harm wildlife.

Blue-green algae’s role in the ecosystem

Like some other algae, cyanobacteria alone aren’t a bad thing. They are naturally present to some extent in every type of water and are major producers of oxygen. However, algal blooms occur when their population becomes out of control. When this happens, not only are toxins produced, but the blooms actually steal oxygen from the surrounding water. This can deplete oxygen from the water, endangering aquatic plants and animals such as fish.

Causes of blue-green algae blooms

Chemical fertilizers that drain into freshwater pools are one major cause of algal blooms. Cyanobacteria are fueled by nitrogen and phosphorus, the two main components of fertilizer. When these chemicals leach into the water, they catalyze the growth of cyanobacteria. Compounded with hot weather and humidity, which all bacteria love, and slow-moving water, algal blooms will flourish.

This is why most cyanobacteria peak in late summer, after the fertilizers applied during the growing season, have had time to reach the water, and the temperature’s at its hottest for the year. Sewage and trash runoff are also major causes of algal blooms because they are essentially providing fertilizer for cyanobacteria, not to mention adding more toxins to the water.

Potential health risks of blue-green algae in dogs 

Cyanobacteria is deadly to dogs. It can be fatal to humans, but animals such as dogs and livestock are more at risk because they’re smaller and less discerning. Unfortunately, dogs may not be deterred by putrid water, so it’s up to pet parents to make sure they stay out of stagnant, green, or foul-smelling ponds.

Symptoms of blue-green algae ingestion in dogs 

If you are concerned that your dog might’ve been subjected to cyanobacteria through swimming or drinking unclean water, rinse them off immediately and take them to the vet for treatment. Although you may not see signs for several days in some cases, symptoms can appear as quickly as 15 minutes after exposure, so it’s absolutely necessary to take them to the vet as soon as possible. Signs of microcystin toxicity include:

  • Diarrhea or vomiting
  • Drooling
  • Weakness
  • Disorientation or confusion
  • Collapse
  • Seizures
  • Breathing difficulties

🚨 If you suspect that your dog was exposed to blue-green algae, do not wait for your dog to show symptoms. Take them to the veterinarian as soon as possible.

How to avoid blue-green algae poisoning 

Unfortunately, you may not always be able to detect cyanobacteria. However, there are a few warning signs that you should definitely be on the lookout for if you’re deciding whether or not to get in the water. When in doubt, stay out.

Avoid lakes and ponds — If it’s over 75℉, opt for a dynamic body of water, such as a river or creek, over a stagnant lake or pond. Your local dog park might also have a doggie pool, or you can buy a kiddie pool to help Fido cool down. Just be sure to dump it out after each use to avoid cultivating cyanobacteria in your own backyard.

Keep an eye out for foamy, dirty water — Adopt the motto, “If it’s not crystal clear, get out of here.” Swimming water shouldn’t look like a frothy cappuccino or a Nickelodeon commercial.

Be aware of foul-smelling water — Beware of water that smells like rotten eggs, low tide, or a wastewater treatment plant. If your dog accidentally dove in dirty water, wash them off immediately and keep an eye out for any unusual symptoms.

While late summer and early fall is the prime time to take a swim, it’s important to be on the lookout for signs of blue-green algae to keep your dog safe. Make sure your dog stays out of stagnant water when the temperature is over 75℉. No matter the time of year, always avoid water that smells foul or has a slimy, green, red, or brown appearance.

Unfortunately, accidents do happen. If your dog got into contaminated water, wash them off and take them to the vet immediately if there’s a chance they ingested it or got it in their nose, eyes, mouth, or ears.

Frequently asked questions

What is blue-green algae?

Blue-green algae is actually cyanobacteria. These invisible bacteria are naturally present in every body of water. They don’t cause problems unless they quickly multiply, leading to HABS (harmful algal blooms). These blooms produce microcystins, which are toxic to people and pets.

How bad is blue-green algae for you?

Microcystins can cause a range of symptoms that affect the digestive, respiratory, and neurological systems in people and animals. If your dog experiences vomiting, diarrhea, difficulty breathing, or seizures after swimming or drinking out of an unclean water source, take them to the vet immediately.

Is it safe to swim in blue-green algae?

No. Blue-green algae is extremely dangerous to you and your dog. While you can’t always detect microcystins, be sure to use caution when swimming in any bodies of water. Always stay out of potentially hazardous water that looks green, brown or red, or smells foul.

Is blue-green algae toxic to dogs?

Yes. Blue-green algae or HABS can cause vomiting, diarrhea, seizures, or even death if not treated quickly.

What to do if my dog has been exposed to blue-green algae?

If you think your dog might’ve come into contact with contaminated water, wash them off immediately and take them to the veterinarian.