Hagener Au

River in Schleswig-Holstein, Germany

54°20′26″N 10°18′19″E / 54.34046°N 10.30533°E / 54.34046; 10.30533 Mouth

• location

Kiel Fjord between Laboe and Stein

• coordinates

54°24′59″N 10°14′32″E / 54.4163°N 10.2421°E / 54.4163; 10.2421Length10 kmBasin featuresLandmarksVillages: Probsteierhagen, Lutterbek, Stein

The Hagener Au (German pronunciation: [ˈhaːɡənɐ ˈaʊ̯] ^ⓘ) is a stream, roughly 10 kilometres (6.2 mi) long, in the district of Plön in the north German state of Schleswig-Holstein. It is an outlet of the Passader See. From the lake's southwestern bay the stream flows in a northerly direction and discharges between Laboe and Stein in the Baltic Sea.

Sections of the Hagener Au are very natural and surrounded by wetlands. In addition the stream is a habitat for the rare spined loach. The stream has been straightened near its mouth and the last 50 metres (160 ft) runs through a pipe. Together with the Passader See the Hagener Au is a protected Special Area of Conservation.