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Figuring Out Blue-Green Algae: How to Spot it in Lakes and Why It Is Unsafe for Dogs

Its Summer! With that comes the unreliable lake water in our area from high bacteria levels to algae. People and their pets, rush for a cool dip in Lake Simcoe and other local bodies of water. Unfortunately, sometimes these waters hide blue-green algae. This article will clarify why blue-green algae is unsafe for dogs and how to distinguish it

Why Blue-Green Algae is Harmful

Cyanobacteria or blue-green algae can release poisons that may turn lethal to people, dogs, and other animals. The two most poisonous poisons from blue-green algae are microcystins and anatoxins. These toxins result in severe health effects, such as:

  1. Liver failure – the cholinergic symptoms being vomiting, diarrhea, or jaundice caused by Microcystins;

  2. Anatoxins cause respiratory failure, muscle tremors and seizures.

Dogs are more susceptible since they can drink from the contaminated water source or even lick up the algal bloom from their coat. The symptoms of this poisoning in dogs manifest within minutes to hours after being exposed to the toxin; hence, the need for a prompt visit to a veterinary office.

How to Identify Blue-Green Algae in Lakes

If you ever want your dog to be safe from danger, you need to view as many factors of blue-green algae identification in lakes and ponds.

Colour and Appearance:

Green, Blue-Green, Brown, or Red Scum: Blue-green algae can form scum on the surface of the water, resembling spilled paint or pea soup.

Surface Mats: These blooms form a thick mat floating on the surface and can be green, blue-green or even brown.

Streaks: Blue-green algae can sometimes form streaks or small clumps on the water.


Grainy or Slimy: Depending on the type, blue-green algae will either have a grainy or slimy texture—like jelly when touched.

Water Condition:

Murky Water: The water will generally become cloudy or murky, mostly GREEN in colour.

Shoreline Accumulation: These algae finally settle along the shoreline, particularly in areas where the water is warm and still or calms down due to poor circulation.


Musty or Earthy Smell: Blue-green algae blooms can produce a musty, earthy, or swampy odour, which sometimes may become a strong indication of its presence.

Practical Tips for Identification of Blue-Green Algae

Visual Inspect the Water: Check regularly for any discoloration or any mat or scum on the surface of the water.

Smell the Water: A musty or earthy smell may indicate blue-green algae.

Avoid Suspicious Water: Avoid contact if you have any doubts about the appearance of the water or if you see visible algal blooms—do not let your dog near it.

What to Do If You Suspect Blue-Green Algae

Keep Your Dog Away: Prevent your dog from swimming in or drinking the water.

Rinse Your Dog: In case of contact with the water, wash your dog properly with clean water to scrub off any algae.

Seek Veterinary Care: If your dog seems sick after being near water, seek your veterinarian right away.

Enjoy the outdoors, but be informed about blue-green algae and take preventative measures to protect your dog. Never take risks around water with your pet. You can check the status of lakes:

If you suspect a blue-green algae bloom, contact the Ministry of the Environment, Conservation and Parks (MECP):


Different pictures of what it looks like.
Blue-Green Algae

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