Beyond the manor house the river is also called the Kühren Au and meanders through meadows to the west of the town of Preetz located on the Postsee lake.

Here it joins the Schwentine, which rises on the Bungsberg and empties into the Kiel Fjord in the Baltic Sea.

Between Postsee and Schwentine the names Postau or Mühlenau (after the old water mill of Preetz Priory which stood nearby) are used.

This use of different names came about as a result of a mistake by the cartographer, Caspar Danckwerth, who, in 1652, gave the real Schwentine — associated with Sventanafeld, the field of battle at the Battle of Bornhöved, different names such as the Bornhöved Bornau, Depenau, Kühren Au and Mühlenau.

A section of the Limes Saxoniae, the fortified border rampart between Saxons and Wends, which was built by the Emperor Charlemagne, ran along the chain of lakes on the Old Schwentine.