The “Schwabentor” embankment on the Dreisam River in Freiburg, Germany was dilapidated and insurmountable for fish. There was no space to build a by-pass for the fish, so a new construction of the bottom structure in was planned in two construction phases. For this purpose, a dam of approx. 2.50 m off-centre which then was rebuild to the finished revetment for the second construction phase. A Bentofix® geosynthetic clay liner was installed. Bentofix® GCLs are needle-punched, reinforced composites that combine two durable geotextile outer layers and a uniform core of high-swelling powder sodium bentonite clay. The Bentofix® GCLs were installed between the existing subsoil and the revetment. Due to the firmly bonded nonwoven layers neither protective nor filter nonwoven was necessary. The result was a near-natural riverbed structure 115 m long and approx. 19.5 to 23.8 m wide. Now all fish can easily get over height difference of 3.3 m upstream.