Press release

dated August 11, 2026, No. 123.

High Temperatures Increase the Risk of Blue-Green Algae in Water Bodies

The Bad Tölz-Wolfratshausen District Warns of Potential Health Risks in Natural Water Bodies

Bad Tölz-Wolfratshausen District. Due to the ongoing heat wave, a massive proliferation of cyanobacteria (“blue-green algae”) may currently occur in any surface water body. At official swimming areas, monthly on-site inspections are conducted during the swimming season from May through September as part of microbiological testing for Escherichia coli and enterococci. During these inspections, attention is also paid to signs of algal blooms. If any abnormalities are detected, further testing may be ordered and, if necessary, swimming bans may be imposed.

Waterways such as the Isar and Loisach are not designated as official swimming areas due to widely fluctuating water quality, varying flow speeds, and other hazards such as whirlpools and weirs. Regular inspections are therefore not scheduled for these areas. There is currently an increased risk of blue-green algae blooms, particularly in poorly flowing side channels, pools, and similar areas.

The District Office urges swimmers, parents, and dog owners to watch for noticeable changes in the water and to exercise caution on their own initiative. Further information on cyanobacteria and how to identify them is available from the Bavarian State Office for Health and Food Safety.

Marlis Peischer
Press Officer / Head of the Press Office
Bad Tölz-Wolfratshausen District Office