The two most important tributaries of the Lahn, and those with the largest catchment inflows, are the Ohm and the Dill. The Dill originates in the southwestern foothills of the Rothaargebirge (the "Haincher Höhe") and enters the Lahn from the right. The Ohm flows from the Vogelsberg and enters from the left. It is notable that not only is the Ohm at the point of its confluence with the Lahn only one kilometre shorter from its source than the Lahn itself, but the Ohm's catchment area of is significantly larger than that of the Lahn above the confluence, , or only before the inflow of the Wetschaft only 2 kilometres upstream.