A mountain stream flows out of Lake Toma in Switzerland, 2,340 metres above sea level. This is the start of the Anterior Rhine. The Posterior Rhine rises (starts) close to the St. Bernard Pass in eastern Switzerland. A pass is a passage through a mountainous area. The Posterior Rhine then goes underground, and the water scrapes away the slate found at this point. This is how the famous Via Mala gorge, hundreds of metres deep, was formed. It is also called the Little Grand Canyon on the Rhine.
The Anterior Rhine and the Posterior Rhine meet at the village of Reichenau in Switzerland. From this point on the river is known as the Alpine Rhine. It empties into Lake Constance at Bregenz in Austria. The water in Lake Constance is of such good quality that it can be used as drinking water.
The start of Lake Constance Rhine at Constance, on the border between Germany and Switzerland, is regarded as the true start of the Rhine. It is from here that the length of the Rhine is measured.