From the mouth upwards to Dehrn (of Runkel), Lahn-km 70 (above Limburg), the river is consistently passable for larger vessels, with locks operated by personnel. The Water and Shipping Administration guarantees a minimum water depth of 1.60 m in the navigation channel. There are stream gauges at Kalkofen (of Dörnberg) (normal water level 1.80 m) and at Leun. Above Dehrn there are manual locks and frequent shoals, making the passage of boats difficult. Two weirs in Wetzlar are an obstruction to shipping further upriver.