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Swimming ban due to blue-green algae – can you still dive?

What are blue-green algae anyway?

Blue-green algae are not algae, they are bacteria. Just like algae or other plants, they can produce the energy they need to live by photosynthesis (using sunlight). In order to carry out photosynthesis, they need certain pigments such as green (chlorophyll) or blue-green (phycocyanin). The name cyanobacteria or blue-green algae comes from this blue-green pigment. Both names describe the same thing. Blue-green algae are bacteria because they do not have a cell nucleus.

Cyanobacteria live in the water all year round, only in very small quantities. In summer, when the water heats up and there are sufficient nutrients such as nitrates (present in fertilisers, for example) in the water, cyanobacteria can proliferate. They can then also reach the water surface and form entire carpets of blue-green algae there. This strong growth is also called a blue-green algae bloom.

The cyanobacteria are everywhere in the water, only in varying concentrations, and migrate daily from the lower water layers upwards and back down again. When they form a dense carpet at the top, they can prevent oxygen from mixing with water and fish can die because they no longer have oxygen to breathe.

Are blue-green algae toxic or dangerous?

The cyanobacteria can also release toxins that can be dangerous to humans and animals. They produce toxins of different strengths and these only have consequences above certain concentrations. Since there are many blue-green algae in a blue-green algae carpet on the water surface, the concentration of toxins is highest there. This is why skin contact can cause a rash, swallowing or inhaling can lead to nausea, diarrhoea, inflammation of the throat, ears or eyes, or allergic reactions. In addition to these consequences, damage to the liver, kidneys or brain could occur if very high doses are ingested.

Can you still dive?

The swimming ban is therefore to be taken seriously, as disregarding it can have serious consequences. As a diver, you wear a neoprene suit, but water still gets under the suit, so you are still exposed to blue-green algae (skin contact). Before diving, you have to swim or walk through the water to the point where you can dive, by which time a lot of blue-green algae will have landed in your regulator.