Danger over for swimmers: what appears to be disgusting, is purely natural – algae
Lake Twiste is clean and free of blue-green algae even if at the moment there is a large amount of filamentous algae present. However, this is not a problem and completely natural, Andreas Gründel, Environmental Engineer from the Hessen State Authority for the Environment and Geology explained. A bather had asked the HAE whether the increase in algae was natural, the algae looked disgusting when he went into the water. A call to the Regional Health Authority was sufficient. “We will deal with it straight away” said Dr Hannelore Wendt, head of the authority.
Said and done, yesterday Gründel, hygiene officer from the Health Authority Heiner Wilke, Manfred Ernde from the Water Authority and Wilhelm Müller from the town council of Bad Arolsen were at Lake Twiste to take stock of the algae situation. While Gründel took measurements, town council workers raked the algae clear for bathers. As a routine, water samples are taken every 14 days. But if there is a complaint, the water is checked again.
Filamentous algae in bathing lakes are always a topic for discussion and often the cause of irritation and annoyance when a lot of them occur. However, filamentous algae are not a recent occurrence but have always been a natural part of the water community. Filamentous algae are a stage between phytoplankton and water plants. “They don’t look nice, but are completely harmless,” said Gründel. “With regard to its microbiological status, the lake is completely normal,” explained Heiner Wilke. For the many bathers at the lake, the depth visibility is 1.2 metres. At the bathing area one can only see down 0.6 m, this being due to the agitated water. The disturbing algae are removed where the bathing area is signposted. At other areas the bathers have to get used to nature in the lake or search for another area. But Müller insists, “we want the bathers to feel good,” and immediately asked the two council workers to remove the algae at the other sites. “Lake Twiste is not burdened by waste treatment run-off,” Manfred Ernde explained, “so there is no danger from that.” This year, Gründel will investigate plankton in the lake for the first time. “Due to the new EU Water Framework Directive one can estimate the ecological potential,” he said. The results will be available under: badeseen.hlug.de.