Blue-Green Algae in your Pond: Warning Signs and Solutions

pet blue green algae toxicity

This article discusses the dangers of blue-green algae in your pond, water garden, river, lake, and other waterways. Warning signs of blue-green algae and common causes, as well as solutions for pond algae control.

What exactly is Blue-Green Algae?

Ironically, blue-green algae isn’t even technically algae at all; the term actually refers to cyanobacteria. Being that cyan refers to a blue-green color, and cyanobacteria very much resembles common algae, the name blue-green algae is the commonly used term.

blue green algae toxic

While similar in appearance, algae and blue-green algae are completely different organisms. The difference: blue-greens are very primitive organisms that are not really algae. They photosynthesize like algae, but they are actually bacteria. Thus, blue-green algae has much more potential to cause harm to an aquatic ecosystem (such as a pond, water garden, golf course waterway, etc.) and even the surrounding people and animals.

How is Blue-Green Algae Dangerous to my Pond and Pets?

While not every blue-green algae bloom produces toxins, numerous studies have shown contact with the bacteria can be harmful. Recent studies have shown the probability that an individual bloom containing AnabaenaMicrocystis, and/or Aphanizomenon (common problem suspended algae) will be toxic is greater than previously thought (45-75%).

Since cyanobacteria toxins can be lethal to pets in relatively small amounts, caution should always be taken when a bloom occurs.

Warning signs of blue-green algae toxicity are: dead fish and/or waterfowl, unexplained sickness/death of a cat or dog, unpleasantly scented water, and skin rashes following human contact with water. Furthermore, one should be cautious in observing pet behavior if worried about the toxicity of an algae bloom.

pet blue green algae toxicity

Common side effects of cyanobacteria poisoning in pets: vomiting, diarrhea, jaundice, seizures, disorientation, coma, shock, excessive salivation, shortness of breath, and death.  With these consequences looming, it is important to be educated and proactive in the fight against blue-green algae.

Learn More About Blue-Green Algae and Dangerous Toxic Algae to Your Pet

How Does it Affect my Pond?

Unlike other types of algae or string algae growth, blue-green algae forms a blanket of slime on the surface of a body of water.  If this layer of bacteria grows enough, it can completely block out sunlight from the depths of the water.  In this way, it can thwart growth of competing algae, and completely dominate a body of water.

If left untreated, blue-green algae can very quickly cover the entire area in a thick, green layer of bacteria.


Facts on Harmful Algal Blooms(HABs) from the Center for Disease Control

  • Dense CyanoHABs (Cyanobacterial harmful algal blooms) can block sunlight and use up all the oxygen in the water, killing other plants and animals.
  • Some cyanobacteria that can form CyanoHABs produce toxins that are among the most powerful natural poisons known.  These toxins have no known antidotes.
  • CyanoHABs can make people, their pets, and other animals sick. Often, the first sign that an HAB exists is a sick dog that has been swimming in an algae-filled pond.
  • Children are at higher risk than adults for illness from CyanoHABs because they weigh less and can get a relatively larger dose of toxin.


In some cases, blooms of blue-green algae have been known to appear seemingly overnight.  This is a result of blue-green algae’s ability to form at virtually any depth of a water body.  These blooms growing at a larger depth can be difficult to identify, creating problematic situations for inexperienced pond keepers.


What can I do to Prevent Blue-Green Algae?

Preventative measures for blue-green algae are similar to those of common plant algae and provide the first line of defense. The main cause of cyanobacterial blooms is the accumulation of excess nutrients in a body of water. The following measures can help prevent a blue-green algae bloom from occurring:

  • Do not overfeed fish or birds; the excess can cause nutrient buildup.
  • Plant and maintain native flora around ponds and streams, which help filter water and don’t require fertilizer.
  • If applicable, properly maintain your septic system.
  • Do not overuse lawn and garden fertilizers, especially near bodies of water.
  • Do not allow pets or livestock to defecate in streams or lakes.

For maintaining a fish pond, learn more ideas in our article on koi pond care in the summer.


How to Protect your Fish, Pets, and Ecosystem!

  • After identifying an algal bloom, keep animals and children away from the pond until it is diagnosed or removed.
  • Scoop out all excess debris and start the damage control process.
  • Use a liquid additive that will balance your pond’s ecosystem while removing blue-green algae.
  • Try not to use an algaecide as these can be dangerous to fish and wildlife.

Choosing a natural solution like Nualgi Ponds will help curtail both the causes and effects of blue-green algae while increasing dissolved oxygen and providing live feed for fish. For ongoing/preventative measures, the 12 essential nutrients in Nualgi Ponds will balance the Nitrogen, Phosphorous and Carbon Dioxide levels to create a more friendly environment for fish and plant health.

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