Algae of a blue hue causes cessation of movement in fish population of Saxony
On August 12, 2025, several water bodies in Saxony and Saxony-Anhalt faced issues with bathing water quality, prompting health authorities to issue warnings and swimming bans.
At the Mockritz Natural Bath in Dresden, a closure was enforced for two days due to an increase in cercariae. These larval parasites, while not posing immediate health risks to humans, can cause a self-limiting itchy rash known as swimmer’s itch or cercarial dermatitis. The rash typically appears within hours after exposure to freshwater containing cercariae larvae of trematode parasites and usually resolves within a few days to about 10 days.
Meanwhile, in Saxony, the Talsperre Bautzen, Koberbachtalsperre in the Zwickau district, and the Kelbra Reservoir in the Mansfeld-South Harz district all reported poor bathing water quality due to blue-green algae. The health authority in Saxony-Anhalt has warned against swallowing blue algae, as it can cause nausea, diarrhea, vomiting, skin irritation, mucous membrane irritation, eye irritation, inflammation, and allergic reactions. Children, the elderly, and people with weakened immune systems are particularly at risk from blue-green algae.
The Kelbra Reservoir in Saxony-Anhalt has also been found to have blue algae near Bitterfeld. The district has advised against swimming at the reservoir and bathing animals also face the risk of poisoning from blue-green algae.
Contrary to popular belief, swimmer’s itch is not a concern at the Kelbra Reservoir, as cercariae mainly affect ducks and other water birds, making it also known as "duck dermatitis." While the condition is generally not life-threatening, it can cause significant discomfort and itching, which may lead to scratching and secondary bacterial infections. In individuals with weakened immune systems, children, and elderly people, the allergic and inflammatory reactions may be more intense or prolonged, potentially increasing the risk of secondary infections or complications.
It is important to note that while immediate medical complications from cercarial dermatitis are rare, discomfort and risk of secondary infections can be higher in children, elderly, and immunocompromised persons. On the other hand, schistosomiasis, a more serious parasitic disease caused by some cercariae species, can lead to severe complications, especially in vulnerable populations.
The Mulde Reservoir, which was previously mentioned, remains closed due to blue algae, while the swimming ban is still in effect at the Kelbra Reservoir. Pet owners should also be aware of the risks posed by blue-green algae to their animals.
[References] [1] Centers for Disease Control and Prevention. (n.d.). Swimmer's itch. Retrieved from https://www.cdc.gov/parasites/schistosomiasis/related_conditions/swimmers_itch.html [2] World Health Organization. (2020). Schistosomiasis. Retrieved from https://www.who.int/news-room/fact-sheets/detail/schistosomiasis [3] Mayo Clinic. (2021). Swimmer's itch. Retrieved from https://www.mayoclinic.org/diseases-conditions/swimmers-itch/symptoms-causes/syc-20369168 [4] World Health Organization. (2020). Schistosomiasis: epidemiology. Retrieved from https://www.who.int/news-room/fact-sheets/detail/schistosomiasis/epidemiology [5] Centers for Disease Control and Prevention. (n.d.). Schistosomiasis. Retrieved from https://www.cdc.gov/parasites/schistosomiasis/index.html
