Retentionsbecken Auhof, Wetland and cultural property in Penzing, Vienna, Austria.

Retentionsbecken Auhof is a flood-retention system on the Wien River at the mouth of the Mauerbach, on about 37 hectares between Hietzing (13th district) and Penzing (14th district). Six basins, Haltung II to VII, lie behind concrete walls on the south side; a 1,300-metre bypass channel runs along the north side, separated by a 6 to 8-metre-high concrete wall whose eastern end is faced with stone and topped by a pylon.

The basin was built between 1895 and 1899 as part of the Wien River regulation project to manage flooding in the expanding city. This infrastructure emerged during a period of rapid urban growth when flood control became essential for Vienna's development.

The name Auhof refers to the site at the mouth of the Mauerbach, where flood peaks of the Wien and Mauerbach coincide. Since 15 June 2001 the six basins and the office building of the municipal Wienflussaufsicht are listed monuments. The distribution weir was modernised in 1956; its original winches needed 24 men to operate.

The six basins (Haltungen II–VII) lie on the south side of the 37-hectare site between the Lainzer Tiergarten and the Westbahn line; a 1,300-metre bypass channel runs along the north side, separated from the basins by a 6–8 metre concrete wall. The distribution weir between Haltungen II and III was modernised in 1956. The site is a protected monument, so stay on the paths and do not enter the basins.

The site was chosen at the mouth of the Mauerbach because long-term observation showed Vienna's dangerous floods arose only when the Wien and the Mauerbach carried floodwater at the same time. The basins were sized for a combined 610 cubic metres per second, of which 400 pass straight on and 210 are held back for up to two hours, giving a volume of 1,600,000 cubic metres.