Algal bloom occurring in the Ilz River

On August 8, 2025, the Passau Health Department reported an increased presence of blue-green algae in the Ilz river near the Halser Dam. The sampling results, which were conducted in the Hofbauerngut area, revealed that the algae had resulted in reduced water clarity.

Blue-green algae can pose a risk to human health, causing skin irritation or allergic reactions upon intense skin contact. Ingesting water from affected waters should be avoided, as it can also be harmful to human health.

Pets and other warm-blooded animals are also at risk from blue-green algae. Therefore, the health department has advised against allowing them to swim or drink from the affected waters.

A bathing ban has been in place for several years in the Ilz river from the power plant in Hals to the Triftsperre due to insufficient water quality. This ban has now been reiterated in light of the recent findings.

The responsible authority for the occurrence of blue-green algae in the area of the Halser Dam is usually the local environmental or water management agency. However, the Passau Health Department has taken the lead in reporting the sampling and findings to ensure public safety.

Swimming in visible algal mats should be avoided, and young children, especially in shallow areas, should not be in the water. The health department advises that people should exercise caution and follow the guidelines to protect themselves and their loved ones.

Water sports in affected waters should also be avoided to minimise the risk of exposure to blue-green algae. The health department will continue to monitor the situation and update the public as necessary.

Residents and visitors are reminded to check the latest updates and advisories before engaging in water activities in the Ilz river near the Halser Dam. The health and safety of everyone is of utmost importance.