Vienna's Old Danube boasts top water quality

bathers on a pier

Thanks to the "Alte Donau" (Old Danube) recreation area, everyone in Vienna can bathe in natural water right in the middle of the city. Water quality has been excellent for many years, and professional aquatic plant management ensures the water remains crystal clear.

The recreation area is very popular with local residents – the water is so clear the ground is visible almost four metres below the surface. The Viennese traditionally flock to the Old Danube in summer. During the swimming season, the water quality is checked in seven locations by Municipal Department 45 - Water Management (MA 45). For many years, the tests have proven a continuously high level of water quality that is comparable with Austria's most beautiful bathing lakes.

Aquatic plants filter the water

They may be unpopular and tickle your toes when swimming, but aquatic plants - so-called macrophytes - are essential when it comes to keeping the water clean and clear. The plants absorb nutrients and thus make sure the Old Danube does not get murky. The oxygen they produce is necessary for the constant self-cleaning cycle of the water.

Underwater "gardening"

Aquatic plants under water

Aquatic plants may tickle your toes when swimming, but they are essential for water quality.

Special care must be taken when managing the natural aquatic vegetation of the Old Danube. To control the development of underwater vegetation, scientific checks are carried out by divers and with sonar devices to monitor the plants' growth. Checks are conducted every two to four weeks from April to October; the results indicate whether and when mowing boats need to be used. The long-term aim is to replace the dominant high-growing plants with low-growing varieties, rendering the use of mowing boats obsolete in the long run.

1,800 tons of plants

mowing boat

Regularly mowing high-growing aquatic vegetation promotes the growth of low-growing varieties. MA 45 has used mowing boats since 2003; on average, 1,800 metric tons of aquatic plants are removed from the Old Danube per year, which equals the weight of about 150 full-size buses. The plants are subsequently composted by Municipal Department 48 - Waste Management, Street Cleaning and Vehicle Fleet (MA 48).

Vienna's strategy of solving natural problems by natural strategies has proven successful over the years. The programme is recognised as an international model project.

Natural riparian vegetation

Professional landscaping methods are applied both under and above water. Water management and planning in Vienna is a challenging task: experts are expected to guarantee top water quality and effective flood control while at the same time keeping the water accessible and providing attractive recreation areas for the local population. The focus is on carefully developing the near-natural riparian environment.

To ensure the banks of the Old Danube become more natural and attractive even where private buildings prevent public access, the City of Vienna offer to provide interested building owners with free planting baskets containing indigenous aquatic plants, such as bulrush, sedge, iris and loosestrife. Experts from MA 45 are happy to provide professional advice and support.


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