Blue-green algae: why are they dangerous and how do they develop?

The first heat wave has reached Germany – and with it the growth of algae in water bodies driven. Especially the so-called blue-green algae are eternal troublemakers – for the environment and us. What makes blue green algae so harmful.

A carpet of algae floats on the Havel River, near Potsdam: The midsummer temperatures of recent weeks have favored the formation of the bacteria in the waters. By the way, living cyanobacteria are green, only the dead ones are blue

Plenty of sunshine, high temperatures and long days make the waters warm: that doesn’t just sound pleasant to us – bacteria also really flourish in these conditions. To coincide with the first major heat wave of the year, the first warnings about blue-green algae blooms in bathing waters were also issued. In contrast to green algae, blue-green algae do pose risks to humans. The name of blue-green algae is misleading, because it is actually bacteria, a type of cyanobacteria.

The problem with these bacteria is that they are toxic and therefore dangerous to humans: "Skin contact can cause allergies in sensitive people. Drinking the toxin-enriched water can cause stomach problems. If it accumulates in the body, it can even be carcinogenic," warns Ulf Karsten, an expert in the ecology, physiology and molecular biology of algae. Dogs or cattle have already died after drinking the toxic water, he said.

There is no automatic ban when blue-green algae appear – only when there is a blue-green algae bloom do municipalities issue a bathing ban. Algal blooms are explosive proliferations.

Nitrogen and nutrients favor the blue-green algae

Blue-green algae are basically always found in very low concentrations in water, under the right conditions they can then spread out. And proper conditions often have blue-green algae: they have few predators and have adapted to many extreme conditions. In addition, blue-green algae would have the advantage that they can absorb nitrogen from the air: "Blue-green algae can do the same thing that some bacteria do in the soil: store nitrogen," explains Dr. Volker Mohaupt, head of department for inland waters at the Federal Environment Agency. Here’s how blue-green algae survive nitrogen deficiencies that occur in midsummer.

Another man-made problem is the addition of nutrients to water bodies. Particularly through sewage treatment plants and agriculture, substances such as phosphorus and other nitrogen enter the waters. These nutrients promote the growth of blue-green algae and other algae and water plants. "In two-thirds of the water bodies there is too much of the crucial nutrient, phosphorus, but reducing the nutrient oversupply is working well," explains Mohaupt. But: less nutrient does not automatically lead to less algae.

Climate change favors stowaways

Expert Ulf Karsten sees climate change as another factor: "The fact that the earth is getting warmer and warmer means that there are already signs that cyanobacteria are also increasing."This heat would add a second problem: invasive species that actually live in tropical areas. "We did our own monitoring and looked at communities of cyanobacteria. In the process, we’ve found some representatives that have taken up residence here – but don’t really belong here at all," says Karsten.

Another problem, he says, is that "there are very few experts. Recognizing a new species and even identifying it as new is therefore difficult," Karsten summarizes the problem. What would help is regular monitoring, but that happens too seldom at the moment – with the amount of ships that reach the port daily. "Customs are overwhelmed."

An invasive species is an animal, plant or bacteria that is not native to any particular place and establishes itself in foreign lands. There, they tend to spread to a damaging degree – bringing with them diseases that the native species are not equipped to deal with.

On a "good way" to reduce nutrients

But what to do against blue green algae? Reducing nutrients in bodies of water is a long process, but one that is on the right track, Mohaupt praised. "Wastewater treatment plants have reduced phosphorus and nitrogen inputs by 75 percent. As a result, agriculture now provides 80 percent of nitrogen and 50 percent of phosphorus inputs to water bodies in."So now it’s up to agriculture, but also smaller wastewater treatment plants, to reduce the supply constantly.

Mohaupt does not currently see any danger from the spread of blue-green algae in flowing water. The situation is different in lakes and dammed rivers: "An algae population needs three days of residence time in reasonably constant conditions to grow up. Once this time is reached in large lakes or dammed waters, blue-green algae blooms can occur, but the danger is much lower in rivers than in lakes."

Are the effects still coming?

In autumn, both the consequences of a green algae bloom and a blue-green algae bloom can cause problems for water bodies, warns the Ministry for the Environment of Rhineland-Palatinate in a press release. By the way, green algae are "real" algae. The so-called blue-green algae have been classified as bacteria in research for some time, since they do not have a cell nucleus. They are among the oldest forms of life. With cooler and shorter days, these die, sink to the ground and are decomposed. If there is typically a strong mixing of the water layers in the autumn, putrefactive gases such as hydrogen sulfide produced during decomposition in the lower part of the lake could be distributed throughout the entire body of water and trigger a fish kill.

Problems for fish also loomed if the pH level in the water rose because of an algae bloom, he said. If the level is between nine and ten or even higher, ammonium can become ammonia, which is also toxic to fish. Especially in shallow waters, the animals would then not be able to escape to other layers.

More harmful bacteria in bodies of water

However, it is not only the blue-green algae that spoil the bathing fun. Other bacteria that get into the water, especially through sewage treatment plants, can also harm us. Bathing sites at bodies of water are inspected by health authorities on the basis of the uniform bathing water guidelines. "The indicator bacterium "coliform bacteria" is used to check whether fecal contamination is present. Increased concentrations of "coliform bacteria" indicate this and thus the presence of pathogens in the bathing water," explains Mohaupt. Then the waters may be temporarily closed for bathing. In 2018, 98 percent of bathing waters met the guidelines, according to the Federal Environment Agency.

But it’s not just bodies of water that have to contend with bacterial infestations. Bathing bans and warnings are also regularly issued for the Baltic and North Sea, especially in summer. In the Baltic Sea, for example, there was an increased incidence of vibrios in the water last year. Vibrions are bacteria that can be particularly dangerous for people in poor health.

Here you can read what the current values of the EU waters are.

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