Alps rivers such as the Danube have major tributaries flowing into them that originate in the Alps. The Rhône is second to the Nile as a freshwater source to the Mediterranean Sea; the river begins as glacial meltwater, flows into Lake Geneva, and from there to France where one of its uses is to cool nuclear power plants. The Rhine originates in a 30 square kilometre area in Switzerland and represents almost 60 percent of water exported from the country. Tributary valleys, some of which are complicated, channel water to the main valleys which can experience flooding during the snow melt
Geography of the Alps passes to the south of the Jura range before reaching Lake Geneva. An area of flat ground reaches from there to Lake Neuchâtel, continuing the border, with the Jura to the north-west and the Alps to the south east. From Lake Neuchâtel to its confluence with the Rhine, the Aare forms the border. The Black Forest is separated from the Alps by the Rhine and Lake Constance, but exact delimitation is difficult in southern Germany, where the land gently slopes up to meet the mountains (known in German as the "Schwäbisch-Bayerisches Alpenvorland", the "Swabian-Bavarian pre-Alps"). In Austria, the Danube runs