In 1816 the Duchy of Nassau and the Kingdom of Prussia agreed to expand the Lahn as far as Giessen, where it joined the Grand Duchy of Hesse. Little is known about the work that followed, but in the 1825 boatmen on the Lahn who shipped mineral water from springs in Selters and Fachingen addressed a letter of appreciation to the Nassau government in Wiesbaden for the rehabilitation of river systems. Overall, however, there seems to have been only repairs and temporary works accomplished through the 1830s.