Until the 18th century, the Upper Rhine was a natural river with a network of ramifications and small river loops (meanders). In the 19th century, the main stream was modified into a regularly flowing, straight and reveted water course with flood dikes. The aim was to make the river navigable and to use the floodplains for agricultural purposes. After World War I the treaty of Versailles (1919) gave France the sole right to use the hydropower of the Upper Rhine. Eight barrages have since been constructed (Kembs, Ottmarsheim, Fessenheim, Vogelgrün, Marckolsheim, Rhinau, Gerstheim, Strasbourg). They interrupt the ecological continuity of the Rhine and are obstacles for migratory fish. The barrages and the power plants Gambsheim (1974) and Iffezheim (1977) are based on a Franco-German treaty of 1969. Today, both hydropower plants are equipped with fish passages.