The Doller river, a Vosges mountain river, rises near the Ballon d'Alsace, flows through Masevaux and into the Ill near Illzach. Its pure, crystal-clear water feeds the water table from which Mulhouse draws its drinking water near Reiningue. Here the path is also a cycle track and is lined with Bysance hazel trees. Before the Doller was dammed up, floods were numerous and devastating.