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Rheider Au (Rejde å, Spangebæk)
Map of the rivers Eider and Treene, Rheider Au and Schlei.
Location
Country	Germany
State	Schleswig-Holstein
Physical characteristics
Mouth
• location	Treene
• coordinates	54°26′48″N 9°19′35″E / 54.4467°N 9.3263°E / 54.4467; 9.3263
Basin features
Progression	Treene→ Eider→ North Sea

The Rheider Au (Danish: Rejde Å or Spangebæk) is a river of Schleswig-Holstein, Germany.

The Rheider Au is a tributary of the Treene near Hollingstedt. Its source is on the Geest near Schleswig. In the Viking Age the route Eider - Treene - Rheider Au - Schlei served as a navigation way and/or transport or trade route between places to the north and the Baltic Sea, as commercial centres functioned (see Dorestad, Haithabu).

• List of rivers of Schleswig-Holstein