Definition: A losing stream is one with a bed, which allows water to flow directly into the groundwater system.
A very famous losing stream in Germany is the Danube. The Danube-spring is located in the Schwarzwald (Black Forest), from where the Danube flows to the east. Near Immendingen and again near Fridingen swallow holes in the bed of the river make the river loose some water. In dry years, the Danube gets completely dry and is reactivated several kilometers away by some tributaries. The water reappears in the Aachtopf.