Water quality of the Alte Donau

Over a million visitors every summer enjoy the clean water of the Alte Donau. Visibility in the lake is up to four metres, and a package of coordinated measures is in place to make sure it stays that way.

The City of Vienna measures the water quality at seven sampling points throughout the summer bathing season. The results have been consistently excellent for many years now: indeed, the water quality of the Alte Donau is comparable to that of Austria's most attractive bathing lakes.

As well as being of high quality from the hygiene point of view, the Alte Donau is also an ecologically valuable body of water. Targeted management of the submerged aquatic vegetation keeps the water clear.

Water plants as a biological filter

They may be unpopular with water sports fans and brush against unsuspecting swimmers, but submerged plants, so-called aquatic macrophytes, are vitally important in maintaining the good water quality of the Alte Donau. They act as a biological filter, binding nutrients and thus reducing turbidity and keeping the water clear. The oxygen they produce maintains the lake's self-cleaning capacity.

The essential role of water plants in the Alte Donau

Underwater "gardening"

In order to prevent tall underwater plants from spoiling people's enjoyment of boating and swimming, the plants are mown by mowing boats to a height that does not bother swimmers or impede boats.

Mowing of aquatic vegetation in the Alte Donau

Restoration in the 1990s and maintenance measures

In the early 1990s there was a huge deterioration in the water quality of the Alte Donau. Comprehensive restoration measures had to be undertaken, and regular maintenance measures have been implemented ever since to ensure that the water quality remains high.

Restoration of the Alte Donau in the 1990s (German)

EU LIFE+ Alte Donau project (2013 to 2018)

Within the framework of an EU project, Municipal Department 45 - Water Management (MA 45) has developed a package of proven and innovative measures to preserve the Alte Donau and ensure that the water quality remains excellent in the future.

The objective of the more than four-year LIFE+ Alte Donau project was to implement an "Integrated Water Resource Management" approach that will safeguard the quality of the Alte Donau for the long term, both as an ecologically valuable beauty spot and as a popular local recreation area. Under the project, a large variety of tried-and-tested measures have been optimised and combined.

The LIFE+ Alte Donau project was funded under the LIFE+ Programme of the European Union as part of the "Environment Policy and Governance" strand.