Sources of the Rhine
The source of the River Rhine is generally regarded to be Lake Toma, in the Swiss canton of Grisons. The lake's outflow, the Rein da Tuma, subsequently becomes the Anterior Rhine, which later confluences with the Posterior Rhine to form the Rhine. Because the tributary systems of the Rhine differ only slightly in length, discharge and the size of their drainage areas, it is difficult to pinpoint a single source of this major European river.
Criteria for distinguishing between main branches and tributaries
There are different criteria for the definition of tributaries, and by some definitions, irrespective of the official name, one strand or another may be called the source. Determining the source of the Rhine is difficult, because in the river system of the Anterior and Posterior Rhine, there are many headwaters of similar size. Apart from the common criterion of the larger discharge, ongoing cartographic research allows us to determine the headwater with the greatest length, the largest catchment area or the highest source.The direction of flow may be crucial to the nomenclature as may be the significance of the valleys as room for housing and transport. Both criteria are more appropriate to the Vorderrhein, since the Hinterrhein valley was hardly populated before the influx of the Walser people.
Rhine sources by name
Image:Rhine source.JPG| thumb | Sign "source of the Rhine" at Lake Toma, with incorrect length indicationThe Swiss Federal Office of Topography and ETH Zürich indicate a point north of Lake Toma and the Rein da Tuma as the source of the Rhine, and as the source of the Hinterrhein a point in the upper valley of the Rheinwald, east of the Rheinwaldhorn.
The course of the Rein da Tuma, after leaving Lake Toma, is not particularly representative: after about, its water is diverted into Curnera reservoir. The water is released at the Tavanase plant and flows into the Vorderrhein at Ilanz. The river begins to be called the Rhine further downstream at the confluence of the Vorderrhein and Hinterrhein near Reichenau and Tamins.
In the area of the headwaters of the Rhine, the term Rhine is used as part of the name of many rivers, in many different spellings, such as Rhine, Rein, Rain, Ragn, Ren, Reno and Rin.
Almost all headwaters of the Rhine are located in Switzerland. Only one of the shorter tributaries of the Hinterrhein, the Avers Rhine, has itself a tributary, the Reno di Lei, which is the outflow of Lago di Lei reservoir located in the Sondrio Province of Lombardy, Italy.
Size of the catchment areas
The catchment area of the Vorderrhein covers about ; the basin of the Hinterrhein, is slightly larger at. The percentage of precipitation flowing down the river is fairly similar in the valleys of the headwaters of the Rhine, so the size of the catchment area tends to be proportional to the average discharge, and therefore this criterion does not need to be considered separately.Summary
Splügen.jpg|thumb|The Hinterrhein near Splügen]No clear hierarchy can be established among the headwaters of the Rhine. The two main systems, the Vorderrhein in the west and the Hinterrhein in the south and east, differ only slightly in length, discharge and size of their catchment areas.
The longest paths begin in the upper Surselva and the upper Landwasser Valley, respectively the most western and the most eastern parts of the headwaters area. The longest headwater of the Vorderrhein is the Reno di Medel, which rises in Ticino.
The source of the hydrological main path would be found in the east, in the Dischma valley of the Dischmabach, although in terms of discharge only, the Aare would be the main river upstream of its confluence with the Rhine, and its source, the Aare Glaciers, would be the source of the river called the 'Rhine' further downstream.