Editing Lahn (section)

=== Marburg-Gießen Lahntal ===
The now southward-flowing Lahn then enters the Marburg-Gießen Lahntal. Shortly before [[Cölbe]], the [[Ohm (river)|Ohm]] enters from the left at the ''Lahn-Knie'' named area. Flowing from the [[Vogelsberg]] through the ''Ohmtal'', the Ohm is the Lahn's longest tributary, with a length of {{convert|59.7|km|mi}}.

The river then breaks through a [[sandstone]] [[mesa]] (the Marburger Rücken to the west and the Lahnberge to the east) into a valley which encompasses the entire territory of the city of [[Marburg]] and its suburbs. The valley begins after the river passes the Marburger Rücken near [[Weimar (Lahn)|Niederweimar]], where the [[Allna]] enters from the right. At the valley's southern end, the [[Zwesten Ohm]] enters from the Lahnberge. The right (western) side of the valley is again formed by the Gladenbacher Bergland, from which the [[Salzböde]] enters the Lahn. On the left rises the Lumda Plateau, from which the eponymous river [[Lumda (river)|Lumda]] flows into the Lahn near [[Lollar]]. Gradually the valley widens into the [[Gießen Basin]].

[[File:Heuchelheimer See.jpg|thumb|[[Heuchelheim Lake]]]]In [[Gießen]], after the inflow of the [[Wieseck (river)|Wieseck]] from the left, the Lahn's general direction of flow changes from the south to the west. The Gießen Basin extends a few more miles downstream to Atzbach, a suburb of [[Lahnau]]. From the 1960s until the 1980s, there was extensive [[gravel]] mining in this area. The area between [[Heuchelheim]], Lahnau, and the [[Wetzlar]] borough of Dutenhofen was to be completely mined and a water sports center with an Olympic-suitable [[rowing (sport)|rowing]] course built. This plan was partly realized, and the Heuchelheim Lake and Dutenhofen Lake are now popular recreational destinations for the surrounding region. Nature conservation organizations, however, were able to prevent further gravel mining, so the area is now one of the largest [[nature reserves]] in Hesse. Dutenhofen Lake marks Kilometer 0 of the Lahn as a federal waterway.

The Gießen Basin is surrounded by the mountain peaks of the Gleiberg, the Vetzberg, the Dünsberg, and the Schiffenberg.  At Wetzlar, the Lahn is joined by its second longest tributary, the [[Dill (river)|Dill]], which has a length of {{convert|55.0|km|mi}}. At this location, the valleys of the Lahn and Dill separate three parts of the Rhenish Slate Mountains from each other: the Gladenbach Bergland, the [[Westerwald]] to the northwest, and the [[Taunus]] to the south.