Effects & Behavioural Recommendations

Possible Effects on Humans

  • Skin and mucous membrane irritation
  • Vomiting/diarrhoea
  • Breathing difficulties, weakness, impaired consciousness
  • Allergic reactions
  • Convulsions, paralysis

If symptoms of poisoning occur, seek medical attention immediately.

Possible Effects for Dogs

Symptoms can appear within minutes of contact with cyanobacteria and can quickly lead to death.

  • Lethargy
  •  Increased salivation
  •  Fever
  •  Vomiting/diarrhoea
  •  Muscle tremors

 If you notice any signs of poisoning, please contact a veterinary practice immediately.

Recommendations for swimmers

Children are at greater risk than adults because they weigh less and tend to drink water or eat sand while playing.

Rule of thumb: if the water reaches your knees and your feet are no longer visible, bathing is not advisable.

But be careful: even in clear water, you may encounter fragments of detached cyanobacteria on the water surface near the shore. 

It is recommended to avoid the following:

  • Algae accumulations (brown, black or dark green) on the shore or pieces or fragments of cyanobacteria floating in the water 
  • Cloudy or discoloured (green, yellow or red) water 
  • Areas where the water smells musty or earthy 
  • Foam carpets or streaks on the water surface
  • Swallowing water

Shower thoroughly with soap after bathing and change out of your wet swimwear.

Seek medical advice immediately if you think you have come into contact with toxins.

Additional Information

Not all cyanobacterial blooms are toxic, and the various substances can vary greatly in their toxicity. In general, cyanobacteria can be harmful to human health at high densities during recreational activities on and in the water, especially for young children. Guidelines from the World Health Organisation (WHO) state that mild symptoms can occur at 20,000 cyanobacteria cells per mL. These symptoms include skin rashes and reddened eyes. If the cyanobacteria count is higher, 100,000 cells per ml, the toxin concentration can reach critical levels, which can lead to breathing difficulties and flu-like symptoms. It becomes dangerous when concentrations of more than 10-100 million cells per mL occur in a section of the lake (usually due to wind) and water is swallowed there. This can lead to symptoms of poisoning such as nausea and diarrhoea in swimmers.

Recommendations for Dog Owners

Ingesting cyanobacteria can quickly lead to the death of your dog! 

Dogs should be kept away from:

  • Areas where the water smells musty or earthy
  • Algae accumulations (brown, black, red or dark green) on the shore 
  • Wooden sticks on which cyanobacteria have formed or to which scraps have become attached
  • Cloudy or discoloured (green, yellow or red) water (including puddles!)
  • Foam carpets or streaks on the water surface

Prevent your dog from swallowing any cloudy water or algae accumulations or licking them off its fur!  

Shower your dog thoroughly after bathing. Seek medical advice immediately if you believe your pet has come into contact with toxins.