The International Commission for the Hydrology of the Rhine Basin (CHR) and EUWID contend that the river could experience a massive decrease in volume, or even dry up completely in case of drought, within the next 30 to 80 years, as a result of the climate crisis.

The variants of the name of the Rhine (Latin Rhenus; French Rhin, Italian Reno, Romansh Rain or Rein, Dutch Rijn, Alemannic Ry, Ripuarian Rhing)[8] in modern languages are all derived from the Gaulish name Rēnos, which was adapted in Roman-era geography (1st century BC) as Latin Rhenus,[note 3] and as Greek Ῥῆνος (Rhēnos).

The spelling with Rh- in English Rhine as well as in German Rhein and French Rhin is due to the influence of Greek orthography, while the vocalization -i- is due to the Proto-Germanic adoption of the Gaulish name as *Rīnaz, via Old Frankish giving Old English Rín,[9] Old High German Rīn, early Middle Dutch (c. 1200) Rijn (then also spelled Ryn or Rin).

The Cadlimo Valley in the canton of Ticino is drained by the Reno di Medel, which crosses the geomorphologic Alpine main ridge from the south.

The culminating point of the Anterior Rhine's drainage basin is the Piz Russein of the Tödi massif of the Glarus Alps at 3,613 meters (11,854 ft) above sea level.

As an effect of human work, it empties into Lake Constance on Austrian territory and not on the border that follows its old natural river bed called Alter Rhein (lit.

Three countries border the Obersee, namely Switzerland in the south, Austria in the southeast and the German states of Bavaria in the northeast and Baden-Württemberg in the north and northwest.

Now flowing generally westwards, it passes over the Rhine Falls (Rheinfall) below Schaffhausen before being joined – near Koblenz in the canton of Aargau – by its major tributary, the Aare.

While it was slightly modified during the Roman occupation, it was not until the emergence of engineers such as Johann Gottfried Tulla that significant modernization efforts changed the shape of the river.

It is a UNESCO World Heritage Site (2002) and known as "the Romantic Rhine", with more than 40 castles and fortresses from the Middle Ages and many quaint and lovely country villages.

In Wesel, 30 km downstream of Duisburg, is located the western end of the second east–west shipping route, the Wesel-Datteln Canal, which runs parallel to the Lippe.

The Rhine-Meuse Delta, the most important natural region of the Netherlands begins near Millingen aan de Rijn, close to the Dutch-German border with the division of the Rhine into Waal and Nederrijn.

Before the St. Elizabeth's flood (1421), the Meuse flowed just south of today's line Merwede-Oude Maas to the North Sea and formed an archipelago-like estuary with Waal and Lek.

For flood protection reasons, the Meuse was separated from the Waal through a lock and diverted into a new outlet called "Bergse Maas", then Amer and then flows into the former bay Hollands Diep.

The northwestern part of the estuary (around Hook of Holland), is still called Maasmond ("Meuse Mouth"), ignoring the fact that it now carries only water from the Rhine.

This meant that high tide formed a serious risk because strong tidal currents could tear huge areas of land into the sea.

Since approximately 600,000 years ago, six major glacial periods have occurred, in which sea level dropped as much as 120 m (390 ft) and much of the continental margins were exposed.

During the so-called Anglian glaciation (~450,000 yr BP, marine oxygen isotope stage 12), the northern part of the present North Sea was blocked by the ice and a large lake developed, that overflowed through the English Channel.

During this time, the lower Rhine flowed roughly west through the Netherlands and extended to the southwest, through the English Channel and finally, to the Atlantic Ocean.

Other factors of importance to the shape of the delta are the local tectonic activities of the Peel Boundary Fault, the substrate and geomorphology, as inherited from the Last Glacial period and the coastal-marine dynamics, such as barrier and tidal inlet formations.

In the geologically recent past the main process distributing sediment across the delta has been the shifting of river channels to new locations on the floodplain (termed avulsion).

The river IJssel branch flows to the north and enters the IJsselmeer (formerly the Zuider Zee), initially a brackish lagoon but a freshwater lake since 1932.

This discharge distribution has been maintained since 1709 by river engineering works including the digging of the Pannerdens Kanaal and the installation, in the 20th century, of a series of weirs on the Nederrijn.

This view is typified by Res Gestae Divi Augusti, a long public inscription of Augustus, in which he boasts of his exploits; including, sending an expeditionary fleet north of the Rheinmouth, to Old Saxony and Jutland, which he claimed no Roman had ever done before.

Augustus ordered his stepson Roman general Drusus to establish 50 military camps along the Rhine, starting the Germanic Wars in 12 BC.

Beyond these rivers she held only the fertile plain of Frankfurt, opposite the Roman border fortress of Moguntiacum (Mainz), the southernmost slopes of the Black Forest and a few scattered bridge-heads.

In the 9th, it formed part of the border between Middle and Eastern Francia, but in the 10th century, it was fully within the Holy Roman Empire, flowing through Swabia, Franconia and Lower Lorraine.

The Alsace on the left banks of the Upper Rhine was sold to Burgundy by Archduke Sigismund of Austria in 1469 and eventually fell to France in the Thirty Years' War.

The Allies' troops left the Rhineland in 1930 and, following the rise to power of Adolf Hitler, the German army re-occupied it in 1936, which proved an enormously popular action in Germany.

In a separate operation, the Ludendorff Bridge, crossing the Rhine at Remagen, became famous, when U.S. forces were able to capture it intact – much to their own surprise – after the Germans failed to demolish it.