The Oude Rijn is a branch of the Rhine delta in the Dutch provinces of Utrecht and South Holland, starting west of Utrecht, at Harmelen and runs by a mechanical pumping station into the North Sea at Katwijk. Its present-day length is 52 kilometres.
In ancient times, the river was the lower part of the main Rhine branch, forking at Batavia Island, now Betuwe, in a northern branche, Rhine and southern branche Maas. It was much broader and was influenced by sea-tides. During occupation of the Romans the river formed part of the northern border of the Roman Empire. In medieval times, river Lek became the main draining river for Rhinewater and the Old Rhine was silting. The river still was important as draining river for the surrounding lowlands, for clay-industry and as a transport and trade route. Ships were towed by horse- and humanpower, using a towpath along large sections of the river, many parts of which have been upgraded to roads over time.