The Upper Lahn with its gravel bank is named after the typical fish of this river region: the grayling. The animal, however, is less and less frequent. The same applies to the gib head. This species is very susceptible to sludge and pollutant contamination of the water body, where the larvae develop in the river’s gravel bed into juvenile fish.

Within the LiLa-LIFE project, special species protection measures will be implemented for rescuing and reintroducing the two fish species, located between Biedenkopf and Marburg to rescue and reintroduce the two species and to investigate their effects.