The principal meaning of the German word strudel is whirlpool. Big Strudel, the vortex near Grein, 94 miles upstream of Vienna. These notorious rapids, 165 feet long and 40 feet wide, were a dreaded hazard in Danube navigation before Empress Maria Theresa had some of the most dangerous rocks blasted out of the river bed in 1853. Now at lowest water, the depth is still six feet in the channel. The Strudel no longer exists.
DeColange, Leo The Heart of Europe from the Rhine to the Danube (Boston, MA: Estes and Lauriat, Publishers, 1883)