The Rhine River (German Rhein, French Rhin, Dutch Rijn) is at 1,320 km (820 miles) one of the longest rivers in Europe. Its name is derived from a Celtic root meaning "to flow". Together with the Danube it formed most of the northern frontier of the Roman Empire and has since those days been a vital navigable waterway, carrying trade and goods deep inland.
The Rhine's origins are in the Swiss Alps in the canton of Grisons, where its two main initial tributaries are called Vorderrhein and Hinterrhein. The Vorderrhein (anterior Rhine) springs from Lake Tuma near the Oberalp pass and passes the impressive Ruinaulta (the Swiss Grand Canyon). The Hinterrein (posterior Rhine) starts from the Paradies glacier near the Rheinquellhorn at the south border of Switzerland. Both tributaries meet near Reichenau, still in the Grisons.
When leaving the Grisons, the Rhine flows north to along the frontier to Liechtenstein and Austria, and then empties into Lake Constance. The Rhine then re-emerges, flows west, mainly on the border between Switzerland and Germany, falls over the Rhine Falls, is joined by the Aar river which more than doubles its water volume, and then turns north at Basel and forms the southern part of the border between Germany and France in a wide valley, before entering Germany exclusively.
At over 800 km, the Rhine is the longest river primarily within Germany. It is here that the Rhine encounters some of its main tributaries, such as the Neckar, the Main and the Moselle. The wider Rhine valley ends at the confluence with the Main and the Rhine then enters a more narrow valley, which widens again south of Cologne. Though many industries can be found all along the Rhine up onto Switzerland, it is here that the bulk of them are concentrated in the Ruhr area, with all of its water draining into the Rhine, causing decreasing though still considerable pollution.
The Rhine then turns west into the Netherlands, where together with the Meuse it forms an extensive delta. Crossing the border into the Netherlands, the Rhine is at its widest, but the river then splits in three main distributaries: the IJssel, the Waal and the Nether Rhine. From here the situation becomes more complicated, as the name "Rhine" no longer coincides with the main flow of water. Most of the Rhine water flows further west through the Waal and then via the Nieuwe Waterweg and, merging with the Meuse, the Hollands Diep and Haringvliet into the North Sea. The IJssel branch carries its portion of the water north into the IJsselmeer, whereas the Nether Rhine flows west parallel to the Waal.
However, beyond Wijk bij Duurstede this waterway changes its name and becomes the Lek. It flows further west to rejoin the main flow into the Nieuwe Waterweg. The name "Rhine" from here on is used only for smaller streams further to the north which together once formed the main river Rhine in Roman times. Though they retained the name, these streams do not carry any water from the Rhine, but are used for draining the surrounding land and polders. From Wijk bij Duurstede, these are first the Kromme Rijn ("Crooked Rhine") and past Utrecht the Oude Rijn ("Old Rhine") which flows west past Leiden into a sluice complex where its waters can be discharged into the North Sea.