An estimated 1.5 million visitors flock annually to the public baths and free swimming spots along the Alte Donau in Vienna, but human activity accounts for roughly 80 percent of the water’s pollution through urine and sunscreen, according to Gerald Loew, head of the department for Vienna Waters (MA 45).
Pollution Sources at the Alte Donau
City officials tracking the health of the Alte Donau have identified humans as the primary source of contamination in the natural body of water. According to Gerald Loew, head of the MA 45 department, human-derived inputs—primarily sunscreen washed off bathers and urine—make up about 80 percent of the lake’s pollution. By comparison, natural elements like leaves and waterfowl account for only 20 percent of the entries.
Loew explained that visitors frequently apply sunscreen right before entering the water, and after spending hours by the shore, some resort to urinating in the lake rather than walking to distant public restrooms. The MA 45 head stressed that natural water bodies are not toilets and urged the public to handle the resource with greater awareness.
Did You Know? The city counts approximately 1.5 million bathers every year across the official baths and free swimming areas situated along the Alte Donau.
Risk of the Lake Tipping and Mitigation Efforts
The accumulation of unprocessable waste poses a severe ecological threat to the Alte Donau. Loew warned that if too much foreign matter enters the water over time, the system can eventually flip or “tip,” a critical state that requires years of intense effort to reverse. The last such tipping event occurred during the 1990s and demanded extensive remediation work to restore the body of water for swimming.
Compounding the pollution challenge, recurring heatwaves are shrinking water levels and raising temperatures, which massively increases the biological community within the lake. To combat dropping levels and warming temperatures, Vienna authorities periodically replenish the Alte Donau with fresh water routed from the Neue Donau. The most recent refill operation took place two weeks ago, raising water levels by 10 to 20 meters.
Expert Insight: Managing urban recreational waters requires a delicate balance between public access and ecological preservation. When natural purification limits are pushed by rising temperatures and human waste, municipalities must rely on active intervention—such as freshwater transfers—to prevent long-term ecosystem collapse.
New Rules and Behaviors for Bathers
To protect the ecosystem, the MA 45 department has issued specific behavioral rules for anyone swimming in the Alte Donau. Visitors are advised to avoid applying sunscreen immediately before entering the water and to use public showers to rinse off beforehand. City water officials emphasize that shifting public habits is essential to preventing another multi-year cleanup effort.
Frequently Asked Questions
What causes most of the pollution in the Alte Donau?
According to MA 45 department head Gerald Loew, about 80 percent of the pollution comes from humans, specifically through sunscreen washed off swimmers and urine.
How many people visit the Alte Donau each year?
The city records approximately 1.5 million bathers annually across the public baths and free swimming areas along the Alte Donau.
How does the city combat low water levels and heatwaves?
Vienna authorities refill the Alte Donau with fresh water sourced from the Neue Donau, raising the water level by 10 to 20 meters during recent operations.
How do you think the city can best encourage swimmers to change their habits at public swimming areas?
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