In Lake Steinhude, one of Germany's largest lakes, the fish population is dwindling. Eels that tradionally have been caught in its waters, are now importet, as their natural migration is hindered. It is discussed, if the lake should be connected to the Weser river system in order to enable fish migration.
For this reason, it was necessary to establish an Underwater Immigration Office for fish in 2016.
On a bridge connecting the main land with an island in the lake, the passerby could get a glimpse into the immigration office through a periscope fastened to the bridge's railings.
Due to the periscope's alignment, there is seemingly water coming through holes in the office's ceiling. The office seems thus to be under water, although its ceiling is really held at the water's surface and the (model-) interior is installed upside-down.