NewsDangerous blue-green algae spread in bathing lakes - this...

Dangerous blue-green algae spread in bathing lakes – this is how they are recognized

Created: 08/09/2022, 06:11 am

A carpet of blue-green algae on the shore of a lake. (Iconic image) © Uwe Zucchi/dpa/Iconic image

Bathing lakes are popular excursion destinations in summer, but in contrast to the open-air pool, invisible dangers lurk in the natural waters.

The summer weather in Germany invites you to go swimming this year. The bathing lakes attract visitors with their refreshing water. As reported, some lakes are so overcrowded that they have to set up parking lot lights or even have to be closed. But the joy of refreshing waters is not only marred by overcrowding. There is a risk of bacteria.

Warning messages about blue-green algae and bathing bans are no longer uncommon this year. But for whom are the algae bacteria dangerous and can they be recognized in the water?

Blue-green algae: This is why the dangerous bacteria are spreading in Germany’s bathing lakes

According to the health department, climate change and a lowering of the still water level should ensure the increased formation of blue-green algae (cyanobacteria) in bathing lakes. The nutrient content in the water should increase due to little wind, lots of sun and high temperatures and thus promote the proliferation of blue-green algae. A high proportion of phosphate and nitrogen in the water in particular causes the number of bacteria to increase rapidly.

Consequences of blue-green algae: This is why they are so dangerous for humans and animals

The dreaded blue-green algae produce toxins, i.e. toxins that can dissolve in the water. If bathers swallow these toxins while swimming or if they come into contact with skin, unpleasant or even dangerous consequences can occur:

  • nausea
  • Vomit
  • Diarrhea
  • body aches
  • conjunctivitis
  • earache
  • respiratory diseases
  • skin rash
  • Fever
  • Allergic reaction

In particular, children, pregnant women or people with weak immune systems must be careful and avoid contact with blue-green algae. But the blue-green algae can also be dangerous for dogs and other animals.

Tip for protection: This is how blue-green algae are recognized in the bathing lake

Some bacteria in water are invisible, but blue-green algae can be recognized by green streaks in the water. They can be seen around 20 to 30 centimeters below the water surface. However, the streaks that form are usually not found throughout the lake, but only in places. The blue-green algae build up particularly on banks, bottlenecks and low areas. A smell of ammonia can also indicate blue-green algae.

A tip from the Federal Environment Agency states that you should go into the water slowly, if possible without raising mud. If you then stand knee-deep in the water and your feet can still be seen, then there is little danger to the bathing fun.

Blue-green algae degradation also feared – fish kills as a result

But when the masses of blue-green algae die off, a new problem arises: when the bacteria break down, a large amount of oxygen is consumed. This lack of oxygen in the water can therefore also become a problem for fish. There is no oxygen in the water. The heat wave threatens fish kills.

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