The Wadi Mujib (Arabic: وادي الموجب, romanized: Wādī al-Mūjib), also known as Arnon Stream (Hebrew: נַחַל ארנון[1]), is a river in Jordan.

The western part of the river is the site of the Mujib Biosphere Reserve, popular for hikes & canyoning amid dramatic rock formations.

This narrow cleft became the bottleneck of an enormous drainage basin of 6,571 km2 (2,537 sq mi) with a huge discharge and annual sediment yield of 143,780 tonnes.

This 1,708-metre (5,604 ft) variation in elevation of its drainage basin,[citation needed] combined with the valley's year round water flow from seven tributaries, means that Wadi Mujib enjoys magnificent biodiversity that is still being explored and documented.

[5] The reserve consists of mountainous, rocky, and sparsely vegetated desert (up to 800 metres (2,600 ft)), with cliffs and gorges cutting through plateaus.

Groundwater seepage does occur in places along the Dead Sea shore, for example at the hot springs of Zara, which support a luxuriant thicket of Acacia, Tamarix, Phoenix and Nerium, and a small marsh.

The reserve is strategically important as a safe stop-over for the huge number of migratory birds which fly annually along the Great Rift Valley between Africa and northeast Europe.

Even under Omri and Ahab, who held part of the Moabite territory, Israel did not hold sway farther south than Ataroth, about ten miles north of the Arnon.

In Roman times, a fort garrisoned by Cohors III Alpinorum, known as Apud Arnona, was situated close to the point where the Via Nova route crossed the Arnon river.