Dangerous cyanobacteria What you need to know about blue-green algae
Lake Neuchâtel, Lake Lugano, Lake Moos and, most recently, Lake Zurich: there are repeated warnings about toxic blue-green algae in Swiss waters. The algae not only spoil the fun of swimming, they can also have unpleasant consequences for humans and fatal consequences for animals. They become a problem when they bloom en masse. The most important questions and answers.
What are blue-green algae and where do they occur?
Even if the common name suggests otherwise, blue-green algae are not actually algae at all. Because these microscopically small creatures do not have a cell nucleus, they are now scientifically classified as bacteria.
These so-called cyanobacteria are not only one of the oldest life forms on earth, as the Eawag aquatic research institute at ETH Zurich explains, but are also "very common" in low concentrations both in water and on land. It is only under special conditions that blue-green algae spread en masse in lakes. Then one speaks of a "bloom". In flowing waters, however, they are not found in critical concentrations.
How toxic are cyanobacteria?
Some, but not all species of blue-green algae contain toxins. They can release these toxins to humans or animals through contact. Their toxins are also in the water that surrounds them. Anyone who swallows contaminated water has the toxins in their body.
There are around two thousand species of blue-green algae worldwide, of which only around 40 produce toxic metabolic products that can be harmful to humans and animals. Some of these cyanotoxins can damage the nervous system or the liver, affect the gastrointestinal tract and the immune system, or possibly even promote tumor growth.
However, cyanobacteria only become harmful to humans - and then especially to small children - when there is a corresponding concentration in the water. Skin contact can cause symptoms such as a rash and red eyes, while ingestion and aspiration of the water can cause breathing difficulties, nausea and diarrhea.
However, the toxins of the bacteria can be fatal to pets and farm animals, especially dogs, if they ingest large quantities of the contaminated water. Sick or dead dogs that have been around lakes are therefore often regarded as indicators that the water is heavily contaminated with blue-green algae.
When is there blue-green algae in the lake?
Cyanobacteria multiply on a massive scale, especially during longer periods of good weather. According to Eawag, the ideal conditions for blue-green algae are in late summer and fall: "calm, warm water, strong sunlight and sufficient nutrients (nitrogen and phosphorus)".
How can I tell if there is blue-green algae in a lake?
- Contrary to what their name suggests, blue-green algae can take on various shades of color. They are often bluish, sometimes grass green.
- Restriction of the depth of visibility and a strong turbidity of the water. The water is milky-cloudy.
- The water often smells musty as the blue-green algae die off quickly. Blue-green algae form stringy, flaky or even spherical accumulations of streaks in the water with a slimy consistency.
- Currents or wind can push them together on the shore to form a dense, creamy carpet, which is why they are often confined to a certain area and are usually localized close to the shore.
Correct behavior if blue-green algae infestation is suspected
- Avoid conspicuously colored areas of water with streaks or flakes.
- People with sensitive skin (including small children) should restrict bathing in the lake to areas with clear water.
- Avoid swallowing water.
- Shower well after bathing and dry thoroughly. - Restrict playing and exercising with dogs on bodies of water to suitable shore areas with clear, colorless water.
- Pets should be kept away from greenish waters. They should neither swim nor drink here.
- Dogs in particular should not be allowed to drink colored water and their fur should be washed out if they come into contact with it,
(Source: leaflet from the Canton of Zurich)
What to do after contact?
If dogs have nevertheless come into contact with suspicious water, the animals should be thoroughly rinsed with fresh water, as cyanobacteria can also be ingested by licking the fur.
If you suspect that you, children or animals have been poisoned by the bacteria, seek medical advice immediately. Typical treatment in humans involves the use of medicinal charcoal. Subsequently, clinical observation is recommended.
What does global warming have to do with cyanobacteria?
Experts assume that climate change will also increase the frequency and duration of cyanobacterial blooms worldwide. In Switzerland, all of the 1,500 or so lakes are affected to a greater or lesser extent by global warming, SRF reported. In addition, sewage treatment plants and over-fertilization in agriculture are also causing too much phosphorus and other nitrogen to enter water bodies in this country. These substances strongly promote the growth of algae.
But there is also good news: in the 1970s and 1980s, blue-green algae blooms were more common than they are today. Various water protection measures reduced the nutrient content in the waters. Farmers have to follow various guidelines when fertilizing.
