The Füsinger Au (German pronunciation: [ˈfyzɪŋɐ ˈaʊ̯] ; also Loiter Au, German pronunciation: [ˈlɔɪ̯tɐ ˈaʊ̯] ; Danish: Fysing Å / Løjt Å) is a river in the north of Schleswig-Holstein (Danish: Slesvig and Holsten respectively), Germany.

The Füsinger Au starts north of Idstedt (Danish: Isted), flows through the lakes Idstedter See and Langsee (Danish: Isted Sø and Langesø respectively), passes the village Loit (Danish: Løjt) and discharges into the Schlei (Danish: Slien) near Füsing (a district of Schaalby) (Danish: Fysing and Skålby).

• List of rivers of Schleswig-Holstein

• flussinfo.net (in German)