The Lahn is a river in Germany that flows through three federal states. It rises in the south of North Rhine-Westphalia and flows only briefly through that state. It soon crosses the border into Hesse and then flows through Rhineland-Palatinate. Before joining the Rhine to the right south of Koblenz near Lahnstein. The length of the river is 242 km. Its catchment area is 5964 km².
It rises in the Rothaargebirge near Netphen. And flows for most of its course through the Rheinisches Schiefergebirge in a rugged basin. Initially it flows in an easterly direction, passing through the town of Bad Laasphe. On the Westphalian side and Biedenkopf on the Hessian side. North of the university town of Marburg, where the Ohm River joins it, it turns south-west. At the university town of Giessen it turns even more to the west and flows through Wetzlar and the residential town of Weilburg. Beyond Weilburg, the Lahn turns sharply southwards .and forms an almost right angle at the village of Aumenau before continuing westwards.
Just after the episcopal town of Limburg, the Lahn enters the Rhineland-Palatinate, flowing through the county town of Diez. Here begins the picturesque Lahn valley, where romantic villages and towns such as Nassau and Bad Ems are found. Lahnstein is the last town that the Lahn passes before it reaches the Rhine. From Wetzlar, the Lahn forms a natural border between the Taunus (south) and the Westerwald (north).
The average water flow at the mouth is 57 m³/s. Flooding occurs in winter and spring. For 148 km from the mouth of the river to the city of Giessen. The river is regulated by locks which allow water transport. The towns of Marburg, Giessen, Wetzlar, Limburg an der Lahn and the spa town of Bad Ems lie on the river.
