As in “The Great White Shark”, the story begins with a swimmer: Ute Scheub regularly climbs into the crooked Lanke in the morning. What is usually a pleasure, but is becoming more and more water zigzag swimming, she writes, “practically no stretch in the entire lake is herb free.”
Creepers were rampant, she says, and then came the big shock: When trying to “pull some of the huge carpets of herbs ashore”, she contracted “pustules”. The plants caused skin irritation.
The reasons for this lie in the depth of the lake: However, non-European organisms caused the strong plant growth, says Stephan Natz, spokesman for the Berliner Wasserbetriebe, which owns the Grunewald lakes. “Everything is to blame for the invasive quaggia shell, Dreissena rostriformis bugensis.”
The storyline of the environmental and perhaps also climate crime story is as follows: The quagga triangular mussel, originally only living in the tributaries of the Black Sea, has been settling in European inland waters for about 15 years and has displaced the domestic triangular zebra mussel.
The problem: “Mussels are excellent water filters,” says Stephan Natz. Since the quagga mussels multiply extremely, they make the water in the crooked lank ever cleaner and clearer. That makes people happy – and the aquatic plants. Because the clearer the water, the more light penetrates into the depth, the better the aquatic plants can grow.
“It grows like hell everywhere”
Better, the aquatic plant: Ute Scheub’s pustules probably come from the rough horn leaf, the water expert believes, that the plant looks like a small fir tree and is up to three meters long. It is tricky that it has no roots, but swims freely under water and spreads further with water movements – caused by swimmers or fish. “It grows like hell everywhere,” says Stephan Natz.
The water companies know both the invasive mussels and the rough horn leaf well, “we really have to struggle with it,” says Natz. It is a huge problem because suction pumps are clogged and have to be cleaned laboriously. A new cleaning rake will now be installed in the Beelitzhof waterworks in order to keep the surface water treatment plant free of plants and mussels.
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Until recently, Stephan Natz did not know that the wild plants in the Krummen Lanke had the upper hand. But last week, an employee of the Beelitzhof waterworks went “on duty”, the result: the rough horn leaf was definitely found to be the culprit, and other swimmers confirmed that the plant felt uncomfortable when touched, says Natz.
Nobody will put on the underwater scythe
What needs to be done now is unclear. On the one hand, “nobody will mow the day after tomorrow with the underwater scythe” in the crooked Lanke. On the other hand, one does not yet know how to keep the quagga shell in check at all. The Leibniz Institute for Freshwater Ecology and Inland Fisheries at Müggelsee is researching the topic, says Natz, but a specialist conference has recently been canceled due to the corona crisis.
The mussel problem is known nationwide. At Lake Constance, the ecosystem suffers massively from quaggas, the stocks of fish from Lake Constance have declined, reports the Bavarian radio. The local water companies try to control the mussel larvae with ozone and sand filters – exit open. For the time being, the following applies when swimming in the Krummmen Lanke: avoid the rough horn leaf as much as possible and above all: do not pull on it.
