The Lenne River is a tributary of the Ruhr River, and has caused flooding in recent years.Having its source on top of the Kahler Asten near Winterberg in an intermittent spring at an elevation of 2,687 feet, the Lenne ends after a course of 128 km flowing into the Ruhr river near the city of Hagen. With an average discharge of 25 m³/s near its mouth, it is the main tributary of the Ruhr.