Elevated temperatures in Brandenburg have led to the proliferation of blue-green algae and parasitic larvae known as cercariae in several local lakes, impacting water quality and swimming conditions. These developments have prompted advisories from local environmental and consumer protection authorities, urging caution among swimmers and visitors to affected bodies of water.

Algae Blooms Compromise Water Quality

During sustained hot weather, certain lakes in Brandenburg are experiencing blooms of blue-green algae, which are actually cyanobacteria. These microorganisms can multiply rapidly when water temperatures rise, especially in combination with nutrients such as phosphorus and nitrogen. The result is a visibly green, cloudy appearance in the water, often accompanied by unpleasant odors. Authorities have noted that blue-green algae are currently affecting the Hohenjesarscher See, Weinbergsee, Vordersee in the Märkisch-Oderland district, and the Groß Glienicker See in Potsdam.

Contact with blue-green algae can cause skin irritation and, in some cases, allergic reactions. Swimmers are advised to avoid areas where the water is visibly green, where algae scum accumulates at the surface, or where dead fish or waterfowl are present. Prolonged exposure or accidental ingestion of contaminated water can lead to gastrointestinal symptoms and, in rare cases, more serious health issues. Children, individuals with sensitive skin, and pets are particularly at risk.

Cercariae Presence and Swimmer's Itch

In addition to algae blooms, certain lakes have been found to harbor cercariae, microscopic larvae of parasitic flatworms. These larvae can penetrate human skin, leading to a condition commonly known as swimmer's itch or cercarial dermatitis. The Grimnitzsee near Joachimsthal and select lakes in Potsdam have reported the presence of these parasites, especially in areas with waterfowl, which serve as natural hosts.

Symptoms of swimmer's itch include itching, redness, and the appearance of small, raised bumps on the skin shortly after swimming. While the reaction can be uncomfortable, health authorities emphasize that the condition typically resolves on its own within a few weeks and does not result in long-term health effects. The best preventive measures include avoiding shallow, vegetation-rich areas of lakes, especially in the early morning or late afternoon when cercariae activity peaks.

Ongoing Water Quality Monitoring

The Brandenburg Ministry for Consumer Protection and the Environment continues to monitor water quality at designated bathing sites. Current data available online show that most of the region's lakes maintain good water quality and remain safe for swimming. However, advisories are regularly updated to reflect changing conditions, including new detections of algae or parasite infestations.

Swimmers and recreational visitors are encouraged to consult official resources before planning trips to local lakes. Authorities stress the importance of adhering to posted warnings and avoiding swimming in areas where water appears discolored, where algae mats are visible, or where advisories have been issued due to parasite risks.

Precautionary Measures for Swimmers

• Check local water quality reports before visiting lakes and adhere to posted advisories.
• Avoid swimming in areas with visible algae blooms or accumulation of surface scum.
• After swimming, rinse skin thoroughly with clean, fresh water to reduce the risk of skin irritation or parasite infection.
• Do not allow pets to swim or drink from affected waters, as they are also susceptible to toxins and parasites.
• In case of skin irritation or symptoms following lake visits, consult a healthcare professional if symptoms persist.

While the majority of bathing waters in Brandenburg remain suitable for recreational use, the ongoing heat wave highlights the importance of monitoring environmental changes and responding to public health advisories. As summer conditions persist, authorities will continue to provide updates to ensure the safety and well-being of residents and visitors to the region's lakes.