Vienna Alte Donau water pollution

In late July 2026 Vienna’s Alte Donau, a major urban bathing site, was reported to be heavily polluted by human‑derived waste. City water authority head Gerald Loew said roughly 80 % of contaminants entering the river stem from swimmers—primarily urine and sunscreen—while natural sources account for the remaining 20 %. The influx of nutrients threatens a eutrophication event similar to the ecological collapse of the 1990s, potentially producing dense algae that could suffocate aquatic life.

Loew urged bathers to shower before swimming and to avoid applying sunscreen directly before entering the water. To offset low water levels and rising temperatures caused by heat waves, the city has been regularly pumping fresh water from the New Danube into the Old Danube, raising water levels by 10‑20 cm in recent weeks. Despite these measures, several swimmers reported gastrointestinal problems, and officials warned that a tipping point could be reached if nutrient loads continue to rise.

The authority continues to emphasize treating the water body as a lake rather than a toilet, and to monitor for algae blooms as a precaution against a repeat of past ecological breakdowns.