River bifurcation occurs when a river flowing in a single stream separates into two or more separate streams which continue downstream. Some rivers form complex networks of distributaries, especially in their deltas. If the streams eventually merge again or empty into the same body of water, then the bifurcation forms a river island. River bifurcation may be temporary or semi-permanent, depending on the strength of the material which separates the distributaries. For example, a mid-stream island of soil or silt in a delta is most likely temporary. A location where a river divides around a rock fin, e.g. a volcanically formed dike, or a mountain, may be more lasting. A bifurcation may also be man-made, for example when two streams are separated by a long bridge pier.
The Hase River in Melle, Germany divides into Hase river and Else river and has been researched as a natural phenomenon.
A bifurcation of the Nerodimka River in the city of Republic of Kosova/Ferizaj, Kosovo, was a hydrological curiosity as separate streams flowed into the Aegean and the Black Sea. The Nerodimka bifurcation was the first hydrological protected object in the former Yugoslavia. The Nerodimka bifurcation is a strict wildlife sanctuary, category I according to IUCN, with an area of 13.0 ha. This bifurcation is considered to be an artificial phenomenon, but created under extremely favorable natural conditions.
In the past, the small Kalaus River in south-western Russia, when reaching the thalweg of the Kuma-Manych Depression at, would split, the two distributaries becoming the headwaters of the West and East Manych Rivers. The former flows west into the Don River and eventually into the Sea of Azov, while the latter flows east, and is lost in the steppe before ever reaching the Caspian Sea. However a dam was built, preventing water from flowing from the Kalaus into the East Manych; thus the Kalaus is now the source of the West Manych only.
The Bahr Yussef is a channel which splits off the west side of the Nile and drains into the Birket Qarun, an inland sea in the Fayum Depression. Originally a natural bifurcation for flood waters, its flow was increased by canalisation in the 12th Dynasty. Around 230BC, the channel of the Nile from which it came dried up, but has since been fed by a new canal to allow water again to make it from the Nile to Al Fayyum. The entire waterway is over 300 km long, consisting of modern canals taking Nile water from Asyut to Dairut, the old Nile channel then runs alongside the Nile for over 150 km to Lahun, then the Ancient Egyptian canal carries the water into the Fayum Depression.
