The State Office of Public Health recommends more caution in bathing places in Berlin, as water temperatures remain warm. Indeed, it is not excluded that mini worm larvae frolic in shallow water. We call them cercariae and we don’t see them. If they infect humans, it can lead to skin irritation, among other things, spokeswoman Silvia Kostner said.
Heavy rains in summer bring some coolness, but they don’t just mean relief for nature. Berlin’s combined sewage system in the city center often cannot cope with the volume of water and overflows. Due to sedimentation, including plant debris, dirt and faeces, the canals of Berlin and other low-flow bodies of water lack oxygen. This can lead to the death of the fish. But Berlin’s swimming spots are also best avoided due to contamination after heavy rains, and it’s best to go for a few days in swimming pools, especially with young children, advises Kostner.
So far this summer, there has been little concern for the bathing spots of Berlin’s lakes and rivers. The water quality is checked regularly. Restrictions were recently imposed only on the airport lake due to a bloom of blue-green algae. This type of cyanobacterium, which glows green rather than blue, is formed as a result of too much nutrients in the water.
When swimming, too high a concentration of blue-green algae can cause skin irritation and nausea. Expect an increase in blue-green algae in warm waters typically starting in late July, Kostner said. On the other hand, it is difficult to measure the presence of cercariae in the water. This can mainly occur in shallow areas overgrown with aquatic plants and populated by snails. This is because the worm eggs enter the water along with the bird droppings and can infect the snails in the shore area. In them, cercariae can thrive, which then swarm as larvae to find their natural hosts – waterfowl.
However, it can also happen that bathers are infected. The cercariae then burrow into the skin and die soon after. Small red spots on the skin that itch easily are then possible. Sensitive skin can also develop papules and severe itching. Sometimes even a dermatologist is then necessary.
According to the state office, waterproof sunscreens and vigorous rubbing with a towel after bathing help prevent it. Wet swimwear should be removed immediately. Evidence of cercariae infestation has already been found in previous years in Krummen Lanke and Großer Müggelsee.
A problem at the bathing area is, however, only caused by humans, added Kostner. The littering piles of garbage attracted rats, which then contaminated beaches, among other things. And some rats also like to bathe. After heavy rains, the helpful bacteria in Berlin’s waterways immediately go to work and break down what has been washed away. To do this, however, they need energy and oxygen. The fish sometimes lack it. Especially at night, when bacteria are unable to photosynthesize and produce new oxygen.
“Two weeks ago, we collected around 2,000 kilograms of dead fish,” reports Derk Ehlert of the Senate Environmental Administration. But that’s little compared to the past, he says. Between May and September, an aeration vessel crosses Berlin at night. Unfortunately, however, fish kills cannot be completely avoided, Ehlert said. The swamp crayfish that immigrated as new inhabitants of the water, on the other hand, are not at all afraid of the lack of oxygen. “They just keep their heads above water.”