The Dreisam is a river running through Freiburg. In the last few years the city has started to renaturate the Dreisam. At several locations fish ladders have been added and weirs have been reconstructed to enable fish migration. Here you can see the reconstruction of one major weir next to a main bridge over the Dreisam: The Schwabentor-Brücke - Bridge of the Swabia-Gate.