Blue-green algae – danger to life for dogs and other animals

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Blue-green algae – danger to life for dogs and other animals

On a walking tour, dog owners allow their three dogs to go swimming in a pond. Less than fifteen minutes later, a dog has severe seizures. The owners immediately take him to the veterinary clinic. Once there, the second of the three dogs begins to show signs of a seizure. Shortly afterwards, the third dog also becomes ill and the liver begins to fail. All three dogs died the very next day. The reason for this tragic incident: The pond in which the dogs were bathed was infested with poisonous blue-green algae.

What happened a few days ago in North Carolina in the USA is also conceivable in Germany: In the hot summer of 2018, several dogs and wild animals in the vicinity of Lake Tegel in Berlin died from blue-green algae poisoning.

What are blue-green algae and when are they poisonous?

Blue-green algae are bacteria with a blue-greenish color. This is where the scientific name cyanobacteria comes from. They are the oldest organisms on earth and can be found in every ecosystem. They produce oxygen and thus supply the living things in the water.

“The presence of cyanobacteria in itself is not a cause for concern,” Thomas Friedl, algae researcher at the University of Göttingen, told Spiegel Online.

It only becomes problematic at high temperatures or when large quantities of agricultural waste products end up in the waters. Because that favors the massive reproduction of blue-green algae. When it blooms, usually in August, the blue-green algae float like a green carpet on the surface of the water. If there is a strong attack by blue-green algae, the toxic effect is very high and especially dangerous for animals and children.

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What health risk does blue-green algae pose for animals and humans?

Blue-green algae are toxic. Bathing in heavily overgrown waters is harmful to animals, children and adults.

Adults who have swallowed too much contaminated water while bathing can get away with irritation of the skin, mucous membranes and conjunctiva, as well as diarrhea and vomiting. In the worst case, it can lead to fever, liver damage, paralysis of the respiratory muscles or even damage to the nervous system. There is a mortal danger for small children who swallow too much contaminated water!

Animals are also at risk: for dogs that eat the remains of the washed up blue-green algae or even lick them off their fur, this can be fatal, as the current cases in the USA and last year’s cases in Berlin show.

Which waters are affected?

When temperatures rise, blue-green algae blooms rapidly. This is what happened in the hot summer of 2018, when so many bathing bans were imposed as it has not been for a long time. For comparison: in 2018 bathing bans due to blue-green algae were in place in 47 German bathing waters, in 2017 there were only 17.

The individual federal states are responsible for monitoring bathing waters. They control the waters and provide online information about relevant bans or issue warnings. You can use the German Federal Environment Agency’s map of Germany to access the relevant websites of the federal states. There you can view lists of bathing waters, bathing water profiles, the results of the quality classifications and current data on water quality in the 2019 bathing season.

In addition, bathers are informed about bathing bans directly at the waters with warning notices.

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How do I recognize blue-green algae infestation?

Relying on warnings is not enough, however. Because the waters are only checked once a month. At high temperatures, however, the quality of the water can change very quickly. Therefore, watch out for signs that indicate that a body of water is heavily infested with blue-green algae.

“Cyanobacteria can swim on the surface of the water. These are then the green streaks. They are to be differentiated from green algae, which pull long threads. Some cyanobacteria form small spheres that can be seen with the naked eye. When you stand knee-deep in the water and yours No longer sees feet, then caution is advised, “advises Jutta Fastner from the Federal Environment Agency in an expert interview on

Blue-green streaks and carpets in the water indicate blue-green algae. © / Cheng Wei

In summary: streaks and carpets in the water that shimmer blue-green are a clear sign of exposure to blue-green algae. Another sign of blue algae infestation can be a bad smell of rotten eggs, liquid manure and ammonia. If the infestation is so severe that you can no longer see your feet while standing knee-deep in the water, it can be very dangerous for animals and humans.

How do I protect my dog ​​from blue-green algae poisoning?

There is only one sure way to protect your dog from poisoning with blue-green algae: If you have discovered blue-green algae in a body of water, then under no circumstances let your dog bathe there! This is the only way to guarantee that your dog will not be poisoned. For unadulterated bathing pleasure, we also recommend:

  • If you regularly go to a body of water on your dog walk, then you can always keep up to date with the competent authority about the water quality.
  • It is imperative that you observe bathing prohibitions and do not allow your dog to bathe in waters that have warnings about blue-green algae.
  • Avoid bathing in places where there are many waterfowl.
  • Put your dog on a leash in infested areas (especially warm, flat, quiet areas of lakes, ponds, and streams that have been exposed to long-term sunlight).
  • If the dog has already entered infested water, make sure that it does not lick its fur or paws under any circumstances.
  • If your dog bathed in a body of water on the walk, shower him thoroughly at home. This will prevent blue-green algae from getting stuck in the fur.
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How do I recognize poisoning by blue-green algae in dogs?

Many dog ​​owners, whose dogs suddenly become very sick and even die, usually do not attribute this to bathing in a lake infested with blue-green algae. Rather, a severe infection or other causes are suspected. So watch out for the following symptoms in your dog. If you notice these symptoms after a recent bathing tour, then poisoning with blue-green algae is likely.

  • Lethargy, weakness and disorientation
  • Pale mucous membranes
  • Excessive salivation and tear production
  • Muscle tremors, stiff muscles, paralysis, seizures
  • Shortness of breath
  • Vomiting and diarrhea
  • Jaundice
  • Shock and loss of consciousness

Blue-green algae poisoning is also very dangerous for cats, horses and birds. Once the animals are poisoned, the course of the disease is dramatic and in many cases ends fatally.