The 6.3 m-high Lahnstein Weir and accompanying hydroelectric power plant, located 2 km upstream from where the Lahn River meets the Rhine River, is an impassable obstacle for upstream migrating fish. Removing this barrier to migrating fishes, especially anadromous species, is an important component of large-scale efforts to rehabilitate the Rhine River system. Due to the spatial and topographic constraints of the site, most technical fish-pass designs or bypass channels were not feasible. In November 1995, a prototype fish collection facility, termed an Aufstiegs-Galerie, was installed and a one-year-long monitoring study initiated to evaluate the efficiency of the entrance. A total of 17,444 fish, representing 20 species, were captured entering the facility.