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With the sun and heat – Danish bathing waters are threatened by algae

The waters surrounding Denmark are all exceptionally warm, with up to 22 to 24 degrees Celsius, they are the perfect growing ground for algae.

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By Bente D. Knudsen     Picture: Bente D. Knudsen

With the heat and sun you may have decided to take a dip in the normally clear blue/green waters at your local beach? Instead you are met by big yellow signs warning of Giftige Alger. 

Unfortunately, the shallow Danish waters are prone to situations with the growth of algae when the sun shines abundantly and the winds for once are absent.

Instead of clear water, you will find it cloudy and greenish in the surface.

This is due to the microscopic algae that float in the oceans, using the energy of sunlight to make food and grow. They float near the water’s surface.

In the right conditions, phytoplankton as they are called, can multiply rapidly, discolouring the water and turning it green or red, they can also create an unsightly and sometimes smelly scum on the surface near the shoreline.

The toxins that some algae produce can affect humans, creating for instance allergic reactions, rashes and nausea or stomach ache.

Small children, the elderly or people suffering from an immune deficiency can be in danger of a toxic reaction, which is why the Danish authorities have decided to put up signs at the beaches warning the public of what to be aware of in order to assess if there is any immediate danger.

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The situation with the algae can change very quickly, as winds and currents may blow them away from one day to the next.

If there is a lifeguard station at your beach, ask the lifeguards, they will be updated about the situation.

Otherwise you can look out for the sign of algae by:

  • when you are in the water at the shallow end and you cannot see your feet – this is a sign of abundant algae
  • if the water is discoloured and unclear

If there are algae in smaller amounts and you do decide to bathe, make sure not to get any water in your mouth, and do not let your dog drink the water.