The earliest attempts to count ship traffic on the Lahn dated from 1827. At the lock at Runkel, 278 vessels were counted in that year, with the state government of Nassau explicitly pointing out that most of the river traffic travelled from the mouth to Limburg, or with smaller boats from the upper reaches to Weilburg, and only a small part passed Runkel. In 1833, however, 464 vessels were counted. The main reason for the increase is likely the increase in iron ore mining in the surroundings of Weilburg. An estimate from 1840 placed the quantity of iron ore transported on the entire river at approximately 2000 boat loads, though the river was only navigable from the mouth to Weilburg. In addition, mainly cereals and mineral water were transported downriver. Upriver, the boats carried primarily coal, charcoal, gypsum, and colonial goods. Around 1835, about 80 larger shallow-draft boats were in operation on the Lahn.